Lecture 1: "COVID-19 and the pandemic"

Hello everyone, we are now nine months into the Covid

pandemic

, in that time a remarkable amount of information has been learned about the new coronavirus and about host cell biology, immunology, epidemiology and clinical diseases. There are complexities to these issues that confuse even experts. The goal of this course is to learn what we know about these topics from the best scientists in the world. I'm Richard Young and along with Fukundo Batista and our teaching assistant Linda Feyen we are lead teachers for the MIT 700 course on Covet 19 Sars Kobe 2 and the

pandemic

. I'm going to make a few comments about the students who are registered for this course and then introduce our first student speakers.

If you miss any of the following instructions, you can find them on the course website. Live first attendance at conferences is recommended, but not. Required recordings of the

lecture

s will be posted with a link on the canvas site. Your assistant will post a message after the conference as a poll to the canvas, the response to which will be required before the start of next week's conference. Responses will be qualified for participation. and students must participate in at least 90 percent of these prompts to pass the class. Lenna will hold a session on Mondays from 1-2 p.m. m., except holidays, to review relevant background material to help you better understand the next day's reading, recommended readings, and other reading materials.

They are posted on the canvas site and will be suggested along with directions. Students are encouraged, but not required, to interact with these materials. Finally, during each session, students can submit questions via the Q feature and the Zoom webinar. Selected questions will be discussed at the end of the conference. and students can ask any unanswered questions during office hours. Our first speaker for this course is Dr. bruce walker The doctor. Walker is a physician-scientist and immunologist, the founding director of the Reagan Institute of MGH MIT and the Harvard Howard Hughes Medical Institute, Professor of Medicine at Harvard Medical School, and Professor of the Practice of Medicine at MIT.

He is also an associate professor of medicine at the Nelson Mandela School of Medicine, University of Kuala Zulu Natal in Durban, South Africa, where he has catalyzed the creation of two major investigations. institutes dr. Apparently, some people can cure HIV infection along with Arlene Sharp. He is co-director of the newly established Massachusetts Consortium on Pathogen Preparedness, a collaboration between more than 500 local scientists focused on Covet 19 research from Harvard Mit Bu Tufts Umass and academic teaching hospitals. in boston bruce thank you very much for giving the first

lecture

in our course well rick uh thank you very much I'm happy to do this um uh well as rick indicated I'm a physician scientist and I graduated from medical school in 1980 uh it came to a mass general with the intention of becoming a family doctor, but then something very strange happened, which was the appearance of a new disease, none of us knew what it was, people who suffered from it were dying left and right, we had no treatments and I It was very clear. quickly that if we, as doctors on the front lines, didn't learn from our patients, then we would see a lot of people die, so I took the route of caring for patients and doing scientific research and kept working. about hiv my entire career and in january of this year, to put this in the perspective that i have on it, i was teaching a course for undergraduates at mit and harvard in kwazulu-natal, south africa, called evolution of an epidemic and this is a course that uses hiv as a model to try to understand how an epidemic arises, how patient clues guide scientific discovery, and how policy and advocacy influence the course of an epidemic now, by chance, one of the Things we did was visit traditional healers. and by chance one of the people in the course was a mit student who had just returned from wuhan and another was the director of emerging pathogens at gilead, a former mentee of mine who had invited as one of the speakers the student from wuhan started to getting text messages several times a day from her family talking about the desperate situation there related to this new um, this new pneumonia that was emerging and Diana Brainard, the person from Gilead, was getting phone calls every day from doctors in China asking.

She asked him to release a drug they had developed for Ebola called remdessevier so they could test it to see if it had any effect on this deadly new pathogen. From those conversations it became clear to me that this had the potential to be a big problem um as rick said I'm the director of the reagan institute our mission is to harness the immune system to prevent a cure for human diseases with a focus on infectious pathogens of importance global and our strategy is really to use interdisciplinary disciplinary collaboration combined with flexible funding to try to make progress and we are fortunate to be embedded in one of the best biomedical research ecosystems in the world so we started working on this immediately and what What I would like to do now as the first speaker is to give you a brief overview of what we know, how this pandemic started, how it causes the disease, the sars cov2 virus, what are the prospects for treatment and what are the prospects for vaccines, so getting right into this, let's put it in The perspective of what we experience with HIV was recognized in 1981, but the infection began to be transmitted in the US at least in 1978 or even earlier, so in 1981 it became Of course something was happening, it was 83 two years.

Later, before we knew what was causing this new disease, it took us two more years to develop a diagnostic test so we could know who had it. Now let's compare what happened with this particular pandemic, so what happened was patients started arriving at the hospitals in Wuhan. with pneumonia of unknown cause and looking back, it was at the end of December when this cluster of cases occurred and there was a really important observation made by healthcare workers and that was that these people had a common experience of having been in the uh in this uh in a hunan market suggesting that this could be a transmissible agent uh um which led to the use of shotgun sequencing to identify the ideological agent and the development of a PCR-based diagnostic test that took four years for HIV to occur in less than a month, so an extraordinary tribute to the advances that have been made in science over the years: sequencing allowed scientists to recognize this as a beta corona virus, which is an RNA virus that It has a single strand of RNA and then an external one. envelope with a predominant spike protein that is an important target for the immune response.

The origin of the virus is almost certainly originally from bats. It is also very closely related to the coronavirus. It has been identified in pangolins, but transmission is probably gone. from bat to pangolin, back to the bad guy and then to humans, although the epidemiology is not yet certain on this, this is not the first pathogenic human coronavirus we have seen. Sars in 2003 caused a total of 8,000 cases with a mortality rate of 11 but fortunately the transmissibility of sars was not so high that it appeared in 2011 and still persists, there have been 2,500 and some cases with a much higher fatality rate. high of 34 but fortunately again the transmissibility is low but look at the contrast with sars kobe 2 We now have 25 million out of 25 million cases as of this morning the estimated mortality rate is between one half and one percent , but it varies widely depending on age group and geography and I think what is important for everyone is very transmissible.

What we need to recognize on this slide is that we can expect to have additional coronaviruses in our future and the great fear and I think what is an existential threat to humanity is the possibility of a coronavirus with the transmissibility of sars kobe 2 and the rate of lethality of mers. So it really behooves us to monitor these emerging pathogens. Why has sars kobe 2 spread so effectively? It is largely because transmissibility begins before the appearance of symptoms and, in fact, this is very different from mers. and sars, which only reach their maximum transmissibility a few days after the onset of symptoms, this makes it very difficult to trace cases and isolate infectious people.

It is not surprising that we have a huge pandemic, 25 million global cases, 850,000 deaths and more than 6 million infections in the US, which is the most effective country in the world, so how is it possible that sars Kobe 2 cause diseases? I would like, because of the diverse audience, to start with a basic concept of understanding what the difference is between a virus and a bacteria by looking here uh e coli compared to sargeras movie 2 size. I've exaggerated the size of the virus here compared to the bacteria, but there are significant differences between these two um e coli has four out of four. thousand genes, like other bacteria, is metabolically active and is capable of reproducing independently. sars kobe 2, on the other hand, has a total of 10 genes and 14 open reading frames, is metabolically inert and cannot reproduce independently, but instead depends on the ability to infect the human host and instruct the human host to actually produce the genes that normally produce proteins for the cell to use for its own purposes, hijack that and force the cell to produce viral proteins so that the virus can replicate and make new copies of itself when the initial infections were identified as being in the lungs, which immediately focused doctors on obtaining samples and trying to find the ideological agent, which is what happened by sequencing long epithelial cells and that also led to a quest to understand how the virus was actually entering the lungs. those cells and that led to the identification of ace2 as the receptor.

There was an advantage to this because this is the same receptor that sars uses in the original sars coronavirus, ie. However, that is not the case, those are not the only cells that become infected: the goblet cells and ciliated cells in the nose are quite infectable and that actually probably facilitates transmission. Lung pneumocytes are infectable, which is how we get pneumonia. The intestine is also infectable and causes diarrhea. In some individuals, the virus can also infect circulating endothelial cells and this leads, as is believed, to a coagulopathy and clotting that results in a great deal of morbidity.

Cardiac myocytes can also express the receptor for this coronavirus and myocarditis has been another. disease that has been observed and it even seems possible that the cells of the central nervous system can also become infected, such as olfactory neurons, this infection does not occur without the body realizing it and one of the ways the body defends itself is that b Cells in one arm of the immune response begin to produce antibodies, which are proteins that bind directly to the virus. They are generated in response to the virus. They learn in the lymph nodes how to recognize it effectively and then attack and destroy it.

The cells become infected and then another arm of the immune system activates so-called killer cells or cytotoxic T cells. They recognize infected cells because, once a cell is infected, it alerts the body to the fact that something bad is happening inside that cell by presenting viral peptides on the cell surface in conjunction with an HLA class 1 molecule, a surface receptor. in these cells foreign peptide in the hla molecule in the junctional groove alerts these killer cells to the fact that something bad is happening, they recognize it and deliver a lethal blow to the cell that kills it and therefore eliminates the infectious virus.

Okay, so we have these immune responses that are generated against this virus in the same way that they do with other viruses, why aren't they doing a better job? It turns out that B cell antibody production is impaired and this is work by Ship Pillai, who will speak later in this course, where he observed through autopsy studies that, in fact, unlike a normal immune response, It is generated within a lymph node where these germ cells are located. The hubs result in antibody maturation, the affinity maturation that allows recognition. What happens in

covid

19 disease is that these terminal centers do not form, so there is an abnormal immune response going on that we are all trying to understand better.

Let me introduce. Now a second concept and that is to make sure that we understand the difference between infection and inflammation. Infection is the invasion of the body by disease-causing agents, their multiplication in the body, and thenreaction of the host tissues to that pathogen. On the other hand, inflammation. It is the body's process of fighting things that harm it, such as infections, by releasing chemicals also called cytokines that call the immune system into action and recruit other cells, so the second reason why the The immune system does not do a better job. It is because it seems that these killer cells are ineffective at eliminating infected cells, but they produce many cytokines, these chemical messengers.

In the same way that infected cells release chemical messengers, these then act on other cells and the activated to trigger even more chemical messengers. and all of this immune activation leads to problems in the bystanders and leads to this hyperimmune state that has been called an inflammatory storm or a cytokine storm and here, looking at a normal lung on the left, you can see the alveolar air sacs, which is where it occurs. the exchange of gases between inhalation and the entry of oxygen into the bloodstream. You can see that they are very thin membranes that allow rapid passage.

On the right, you see what happens in the Covid19 disease. There is this. Massive infiltration of inflammatory cells marked thickening of the septa and impaired gas exchange, leading to clinical problems with lung disease. Basically, what I just told you is that we have an immune response designed to basically generate an antiviral immune response and that happens from the beginning, but what we believe happens in Covet 19 disease is that it is actually replaced by an inflammatory response from the host who actually, instead of acting as a friend, actually acts more like an enemy in the later stages of Because the severity of the disease is increasing, we know that this disease does not affect everyone equally, it is probably not surprising because the older people get, the more likely they are to have comorbidities that make them less resistant to disease in general and, in fact, what it was.

What was surprising from the beginning was the feeling that children were not getting infected, but unfortunately that is not true and, in fact, in the data that just came out yesterday from the American Academy of Pediatrics, there has recently been a further increase in cases, hospitalizations and deaths, a percentage increase in children compared to the percentage increase we have been seeing in adults, on top of that, there is a unique inflammatory syndrome that has been recognized in children that is similar to Kawasaki disease, which is an inflammatory disease of unclear etiology, but what can be seen on This slide is that between 2015 and 2019, before the arrival of Covet 19 disease, there were sporadic cases of non-severe Kawasaki disease and occasional severe cases, but look what happened in 2020, suddenly, this huge increase in infections we believe is due to a post-inflammatory or post-infectious inflammatory response, what exactly causes it is still being investigated, but it is critically important in relation to the development of vaccines for children .

I'd like to say a few words about diagnosis now as a key component of trying. To reduce the pandemic, you are probably most familiar with RNA testing, which is PCR, and this is what is being done through the broad Institute for all undergraduates at MIT and Harvard. These RNA tests use the polymerase chain reaction to amplify fragments of a virus. RNA, so they don't tell you if what is being amplified is actually infectious or not, they just tell you that there is viral genetic material there and if you look at how it was done in the mass general hospital with RNA detection rates after admission to hospital.

In the hospital, what you see is that the percentage of people admitted who start out testing positive decreases over time, but some people remain positive for four weeks or more. The question is whether these people are infectious all that time because right now we are using the RNA detection assay is a yes or no assay. It turns out that infectiousness is declining over time to the point that the CDC revamped its definition of recovery to mean 10 days after symptom onset and at least three days without symptoms is really critical. We developed an assay that we don't have yet that tells us that it measures the infectiousness of a person now another diagnostic test that has been developed is called it's a category called antigen tests where you're not looking for biogenetic material, you're looking for viral proteins, like the uh membrane proteins in blue or the spike protein in brown here and the way these diagnostic tests are performed is very similar to the point of care diagnostic test that is used as a pregnancy test. where what you do is put a detector strip in the urine in the case of a pregnancy test and in the case of um wait and in the case of

covid

19 the ideal would be to use a saliva or a nasal swab and then use a swab which will tell you if you are infected or not by having one or two bands on this strip illuminated.

They are now available. They are less sensitive, but in fact, less sensitive may be better. Just think about the different assets I just told you about: RNA-based tests are much more expensive and require much more extensive machinery, although that is also being addressed. Rapid antigen tests are much cheaper. The sensitivity is lower, but it is expanded. The capacity is greater. It is easier to reach underserved areas. It is easier to test frequently. They are moving forward to do it and there are problems in the supply chain that are predominantly for the RNA test but not so much for the rapid antigen tests, so another important diagnosis is to determine who has already had the infection and this is done through antibodies which are proteins in the blood that are generated in response to an infection when someone is initially infected, a wave of virus occurs, the immune response responds by generating antibodies and ideally these antibodies then, once the infection is eliminated, drop to a level and they persist to protect against subsequent infection in the future, if you look at the antibody responses in people who are hospitalized in the same cohort, you can see that they slowly increase over time and in about three weeks almost everyone has antibodies, so you feel it, so we have. ways to actually track the infection, find out who is infected, and these antibody tests are going to be a really important epidemiological tool, let's keep talking about what the treatment prospects are, basically there are two approaches that in general, they are looking at antiviral therapies that attack directly to the virus and, an example of this, is rem degrave.

Remember at the beginning I told you that Diana Brainerd was getting calls in South Africa to launch a drug that had been developed for Ebola. that drug was administered harshly and has now been shown to have some effect. The important thing to note from this article that was published in the New England Journal is that although Remdesseviere has an effect on speeding up recovery time, there is no change in mortality that is statistically significant, so it is actually a marginal benefit and should be administered intravenously. We need drugs that can be administered orally, that can be administered early in the onset of the disease or at a later stage of the disease, and that have an effect that is likely to have an effect.

There is a big difference when drugs are given in terms of their ability to produce an effect and I will say again that another approach is to use neutralizing antibodies against sars kobe 2 and these can come from convalescent plasma that has been granted an EUA. emergency and There has been a lot of controversy as to whether it really works. Another therapy on the horizon is monoclonal antibodies that can neutralize the virus and could be administered prophylactically or potentially therapeutically, but are not yet licensed. Another way to approach therapy is to have targeted therapies to block the cytokine storm, so these are host-directed therapies, such as antibodies against interleukin 6, which is elevated, it's a pro-inflammatory cytokine and it helps create this cytokine storm. cytokines, and another is dexamethasone, a steroid, dexamethasone has been shown to have some effect and is now being used, but there are many, many trials going on and there is still no favorite drug that really meets the requirements that I think the impact of being easily available and ingestible orally.

It acts quickly and is active during all phases of infection, so let me go on now to talk a little bit about what the outlook is for vaccines, which is really what I think it's going to take to get out of this pandemic again. concept to make sure that we are uh our basics to make sure that we are all on the same page immunity is protection against an infectious disease if you are immune to a disease you can be exposed to it without getting infected or you can have a very attenuated infection, so that you don't even realize you have been infected, immunity can be induced by at least two different mechanisms, one is the infection itself and hopefully leads to immunity for any subsequent encounter by generating, for example, antibodies. that persist, another is through immunization, which is the administration of a vaccine product that stimulates a person's immune system to produce immunity to a specific disease, protecting that person from the disease;

In other words, you are training the immune system to attack the virus without the person having ever seen the virus by giving only a portion of the virus in a vaccine and using it as a training vehicle, so right now there are probably about 200 vaccines in development in terms of where we are in human trials. There are a large number of vaccines that have already entered human trials. 23 vaccines are in phase 1, which is the first phase of the study to test whether the vaccines are safe and determine what type of dose can be tolerated. Phase two: There are now 14 vaccines in that stage, which is an expanded expansion of the phase one trial to get more safety information and learn something about immunogenicity.

Phase three trials, of which there are nine, are when the large efficacy trials begin. I think you've all heard that the goal is to determine the effectiveness of a vaccine as quickly as possible, and the way to do that is to dramatically increase the number of people who receive the vaccine, so that the planned trials are between 30 and 50,000 patients. , because it has to be done. There have been enough infections to show that the approved vaccine works better than the placebo. Finally, there are three vaccines that have been approved for limited use before, not by the FDA but by other countries, China and Russia in particular, but there are no approved vaccines yet. for full use, four different general categories of vaccines are being pursued: one is the genetic vaccine, the modern vaccine here in Boston is one of those that is based on messenger RNA and DNA.

It is another way of using one or more genes to stimulate an immune response. inactivated uh sars cov2 viral vector genes is another approach that is partly being done here in boston by dan baruch in collaboration with jansen and also by astrazeneca in collaboration with oxford. This is the use of another virus to deliver v2 genes to cells to stimulate an immune response. A more standard approach that has been used for years is viral protein plus adjuvant. This is a little further back in the process, but uses cyrus cov2 protein or protein fragment along with something to help stimulate the local environment where the injection is given. to stimulate an immune response and ultimately inactivate sars cov2, which is just the inactivation of the entire virus, which has also been used in the past and is what the Chinese have already started using in some circumstances, let me tell you a little bit about what Which we know from the work we've done here in Boston.

This has been led by Dan Berut, one of the founding members of the Reagan Institute, who is also a physician-scientist and at Beth Israel Deaconess Medical Center as soon as the virus appeared. The sequence was published and synthetic genes were ordered. The design of the vaccine began based on an existing collaboration with Jansen Johnson. Johnson worked together at the end of January, then tested the vaccines on animals during February, established a challenge stock and, by the end of March, had data. suggesting that this was immunogenic in monkeys and Jansen made the decision to move forward with increased production in case subsequent studies showed them to be safe and effective, the first human studies will be carried out in this month and the expectation is that by early 2021 there will be a massive scale-up and emergency use authorization for the vaccine.

Here is the data from the monkeys in the mock vaccination on the left. Red is the compound for 10 animals. You can see there is a markup. increase of the virus in this case after vaccination and after the challenge, but on the rightYou see the marked difference using the spike protein as the vaccine antigen and of the four animals that were in these two I actually never had a problem in the virus and two of them had a markedly attenuated level of virus in the bloodstream, so The goal here is that, instead of what happens with infection, where an antibody response is generated, what will happen here is that through vaccination.

We will generate antibodies and then once, if the person encounters the virus, what will happen is minimal infection or in fact no infection related to a massive increase in antibodies when they encounter the true virus infection, so what? How will we know if a vaccine? is it effective, well we have to test it in a place where there is a lot of transmission and unfortunately in the world there is still a lot of transmission, most of it in Asia, but also in South Africa, South America and North America, and increasing numbers . In Europe and the New York Times on the front page this morning there was an article about the concern in Spain that there is an essence of recruiting new cases.

In South Africa there has been a significant increase, but it has decreased, but we also know that it is due to a broad restriction of activities. As shown in the New York Times vaccine tracker, we're seeing a lot of cases of infection in uh being detected at universities, which may be another place to test a vaccine, although many of them are actually turning more to education online for Moving forward, ultimately we will have to prioritize and decide. What are the vaccines that we really want to take and what do we really want to push to make 7 billion doses so we can make them available to everyone?

The only question is: will a vaccine protect against infection or against or? Does it simply protect against disease? And ideally we would like to have a vaccine that completely protects against infection, which would be an antibody-based vaccine to release the virus before it can infect cells, but even something that protects against disease and keeps the virus low enough. that people who will not transmit would be extremely beneficial and that would probably depend on the T cells, how many doses are needed for protection, well, if it takes three doses given over six months to get protection, that means there is a vaccine available to give . in December it won't actually protect people until next June will there be enough new infections to show that it protects?

I just went over how soon the vaccine may be available and here I think you have to be aware of when the first vaccine will be given. it's in a vial and it can be given to a person versus when that vaccine is available around the world and you can go to your doctor's office and he has it on his shelf and he can take it from you and give it to you And that will require a massive scale-up and I think that we all hope that multiple vaccines will reach the goal because none of them will easily reach the level of seven billion doses of the vaccine that they give. baruch is doing with the reagan institute and bi dmc the um, they have committed to manufacturing a billion doses, um, so the next issue is enough with the vaccine that is being manufactured, it's going to be a challenge, but people are expanding on that right now, a critical point. and a critically important question is whether the vaccine works regardless of age.

Most vaccine trials do not include much older people. The few that have done it in humans have shown that people who are more susceptible in terms of age are less likely to develop immunity. response to the vaccine vectors that have been given, another critical question is whether a vaccine requires a cold chain and this is really critical when you think about global delivery if you have to keep the vaccine on dry ice and you have to deliver it to rural areas of Africa, also, if you have to give out aliquots of the vaccine once it gets to the community that you're trying to administer it in, that requires special facilities and special measures that will make it much more difficult, so ideally I don't want any cold chain requirements.

How long-lasting is the immunity induced by the vaccine? Well, there have already been some suggestions of reinfection of people who have already been infected. Shiv Pillai's work suggests that the antibodies produced are not normal in that sense. The lymph nodes themselves are not normal, they do not have germinal centers generated, so I personally think that the word is still getting out, or it is still not clear whether these immune responses generated by natural immunity actually provide long lasting. long-term protection and time will tell Another critical question is: do vaccine-induced antibodies improve infection or is it possible that they may even contribute to multifocal inflammatory syndrome in children?

And another thing that's not on this slide is that, in fact, children are still people. Those under 18 years of age are another category of people who are not being tested properly at the moment in the first wave of these vaccines, as we look for safety, but when the trials are carried out in people from 18 to 65 years of age. In the old days, the question is whether you're going to need to do a whole set of separate studies in children to get a license to give these things to kids and know that they're safe for kids, so this is a really important point.

That I don't think has been given enough attention, at least it's not clear from what I've read what the actual plans are for the development and licensing of these vaccines for children, so I think while we're waiting for a vaccine, we have to ask ourselves What else can we do. For us in the Boston and Cambridge area, I think a group of scientists recognized that this was going to be a really challenging problem and we felt like we actually had something to contribute. We felt like we had something to contribute on a larger scale if we could get everyone to collaborate together, so on March 3rd I had, uh, I think what for all of us was a really unique experience where we met with about 85 Harvard scientists. mit Umass Tufts. and Boston University to talk about what we as a scientific community and the clinical community could do to address this pandemic and what came out of that was the establishment of the Massachusetts Consortium on Mass Pathogen Preparedness CPR, which has been an experience extraordinary for everyone.

Of us involved I have never seen the type of collaboration that has evolved from this consortium. We have six different working groups in areas ranging from clinical and outcomes research to diagnostics, therapeutics, pathogenesis and vaccines and epidemiology, um uh, and a lot of collaboration and sharing has been happening, too. We've been collaborating closely with researchers in China who are at the Guam Show Respiratory Health Institute, which has been a fabulous collaboration and I'm really optimistic. Given the number of people working on this problem and the selflessness with which people have been working, we will make real progress in the future.

I think we've already seen extraordinary progress to this point. I think the other thing we can do is move forward. In science we know how transmission occurs and there has been a lot of talk about droplets versus aerosols and how long they stay in the air, etc., but I think the critical experiment has actually been done and the fact of the matter is that we know how to prevent the broadcast. and that experiment was done in hospitals where everyone was wearing masks, you couldn't really achieve distancing, but hand washing could, and what we didn't see were major outbreaks among healthcare workers, in fact, overall, the incidence of infection among health professionals.

There are fewer workers than in the community, I think that shows us that masks work and I think as we all work as vigorously as we can to find solutions in terms of therapies and vaccines if we wear our masks. We will prevent transmissions from occurring, so let me draw some conclusions: one is that advances in other fields have clearly accelerated responses to Covet 19. Everything we have done at the Reagan Institute has been based on what we learned working on HIV . including the entire backbone of dan's vaccine, sars kobe 2 infection is transmitted before symptoms appear, which is how it spreads so quickly and why it's so important for everyone to wear masks, the infection produces a hyperinflammatory state which involves multiple organs and that is what makes us believe that it contributes greatly to the pathogenesis: currently there are no highly effective treatments, although there are some that have a marginal impact, but we really need better drugs and while we wait for a vaccine, it can be achieve effective prevention with masks, physical distancing and hand washing there has been unprecedented progress towards a vaccine, we have to be sure that that vaccine is safe and effective so when we actually administer it more widely and clearly, there is still a long way to go to do and a lot that people, regardless of their discipline, among The students who are listening to this talk come across a pandemic, whether in the scientific field, the psychological field, the therapeutic field, the economic field, etc. , so that we can all contribute to a solution, and with that, I will thank you. for your attention and I will be happy to answer some questions, Bruce, thank you very much, the students have several questions, one asks you, why do you think the United States is among the most infected nations in the world?

I think you can really see that in the tracking that I've shown over the last month, the number of infections has decreased in the US and that is directly related to greater adherence to mask wearing and social distancing implemented in other countries . those measures immediately did complete lockdowns like we did, but they came back from the lockdowns with continued and very vigorous compliance with the prevention measures that were available to us, you know, and it's not really a surprise that masks are important in In fact, it is important that you wear a mask to protect other people.

I don't think anyone on this call wants to have open heart surgery with their surgeon and our nurse, not wearing masks, they don't. They use them because they are afraid of contracting an infection from the patient. They use them to avoid infecting the patient. We know that masks can do that, so I think that's a critical factor here and one of the unknowns for the future as to whether people will actually adhere to that and whether people will understand that there are times when we need to limit our own freedoms to protect the general population, and there are many examples of decisions that we, as a society, make to do just that and I think this is a situation where we must do the same and Tara asks how long after recovery of the infection the antibody test results are still positive, so this is a really critical question and unanswered yet, so we will only know as long as the epidemic has existed and there is evidence that in some people the levels of antibodies are declining to become undetectable in a fairly short period of time.

There is concern, I alluded. for at least four cases of presumed reinfection of people who have already been infected, presumably because we have very good evidence that antibodies can be protective if they are there, but these people have been reinfected, we don't know. your antibody levels to really know how it correlates, but that's a big concern and obviously that would have a big impact on the development of herd immunity, which is when enough people have immunity that others don't, and the virus can't easily. it is transmitted through a population because there are not enough there are not enough susceptible hosts now the question that was asked was if someone gets infected, how long do those antibodies last now?

I think the data that shiv generated suggests why they may not last long, but what about immunization? Well, how long will those antibodies last? And that's something else that we don't know, but my feeling is that it's probably going to last longer because instead of trying to generate an antibody response in a lymph node in this one that's infected with live virus in this case you're taking a fragment of virus by delivering it to a lymph node and the lymph nodes learn to know how to teach the immune response to recognize it without being affected by the ongoing replication of the virus, so I think it's probably two very different things, but real time will tell when Lennon asked if he could comment on the mutability of the v2 source code and the impact of mutations on our vaccination plans.

Yeah this is another very good question so sars kobe 2 is nothing like uh hiv. which mutates at an incredible rate, in fact, if I compare a sequence of the hiv uh virus from Boston to one in South Africa, there may be 40 different ones on the envelope, so we've never dealt with trying to make a vaccine. to such a pathogendiverse in contrast to our cov2 uh it has very few mutations, it mutates and the consequences of those mutations on immune recognition are still being resolved, but there is concern then and clearly, the entire population, the global sars population has already done so. has changed to some extent and I know that Dan has already made another vaccine with a second strain of sars, just in case, what will be critical is whether the mutations that arise, although we hope they will be much smaller than with hiv, if in reality results in immune escape and again, this is one reason why we need to do a lot of sequencing and a lot of surveillance to get ahead of this um and um and it may be that like other infections like influenza, there is a requirement for um to update vaccines on a regular basis, having another student request the genetic vaccine, or vaccines that use an inactivated viral vector, are concerns about the long-term effects of the vectors or delivery methods, so with genetic vaccines you know that there is less experience with them and So, the clinical trials that are ongoing now for other diseases, for example, modern disease, have other pathogens for which they have developed vaccines, so they have more data in humans from those DNA vaccines.

Likewise, they have been used for other pathogens, so data have been generated. In terms of inactivated viruses, we have used them for years. You know, you can ask, do you know why we didn't do that approach with HIV? In fact, in the monkey model it looked like an inactivated virus worked, but the concern is just whether the virus could somehow reactivate and become infectious and I think that's a moderate enthusiasm for inactivated vaccines, but I think there are ways to make an activated vaccine safe and um, but that's the main concern. Another concern is that it is more labor-intensive.

And it's expensive to make inactivated vaccines because you have to develop a lot of virus to be able to do it and these completely synthetic approaches that you can use like with mRNA are potentially a real advantage if we can do it without having to do it. Relying on cell culture and other aspects that are required for more traditional approaches, many students had questions about reinfection and the possibility that reinfection is a consequence of antibodies simply not doing what they are supposed to do. Do you have an opinion on reinfection, how, to what extent it happens?

Yes the implications are like that and there is another concern about reinfection based on the dengue virus uh and that is whether the antibodies could actually make things worse the second time around. One of these cases of reinfection, so as not to alarm people, seemed to be worse the second time. but so far there is no evidence from the above sars data that i think is convincing. There is no evidence to suggest that this antibody-dependent enhancement phenomenon exists. I think in terms of protection against infection, the antibodies will have neutralizing antibodies. You will be required to do that upon reinfection, so not everyone generates sufficient levels of neutralizing antibodies, probably from their first infection.

However, I think T cells can also play a very important role in cases of reinfection because if the virus slips through. through the first defense of antibodies and enters the cells, then the t cells are the main effector mechanism that can eliminate the virus, so I think the attention to vaccines that not only produce antibodies but also produce cells t is important, furthermore, there is a second type. of the uh t cells, in addition to the killer cell, those are helper cells that help orchestrate an effective antibody response in those germinal centers and therefore generate specific and coveted helper t cell responses, I think that may also be really very important, particularly for perspective. of possible reinfection Bruce, we really appreciate you giving us an introduction to the disease, the virus, the pandemic.

Thank you very much and we will see you all again next week. Thank you so much. Enjoy it.