Posted on by Dr. Francis Collins
A key issue as we move closer to ending the pandemic is determining more precisely how long people exposed to SARS-CoV-2, the COVID-19 virus, will make neutralizing antibodies against this dangerous coronavirus. Finding the answer is also potentially complicated with new SARS-CoV-2 “variants of concern” appearing around the world that could find ways to evade acquired immunity, increasing the chances of new outbreaks.
Now, a new NIH-supported study shows that the answer to this question will vary based on how an individual’s antibodies against SARS-CoV-2 were generated: over the course of a naturally acquired infection or from a COVID-19 vaccine. The new evidence shows that protective antibodies generated in response to an mRNA vaccine will target a broader range of SARS-CoV-2 variants carrying “single letter” changes in a key portion of their spike protein compared to antibodies acquired from an infection.
These results add to evidence that people with acquired immunity may have differing levels of protection to emerging SARS-CoV-2 variants. More importantly, the data provide further documentation that those who’ve had and recovered from a COVID-19 infection still stand to benefit from getting vaccinated.
These latest findings come from Jesse Bloom, Allison Greaney, and their team at Fred Hutchinson Cancer Research Center, Seattle. In an earlier study, this same team focused on the receptor binding domain (RBD), a key region of the spike protein that studs SARS-CoV-2’s outer surface. This RBD is especially important because the virus uses this part of its spike protein to anchor to another protein called ACE2 on human cells before infecting them. That makes RBD a prime target for both naturally acquired antibodies and those generated by vaccines. Using a method called deep mutational scanning, the Seattle group’s previous study mapped out all possible mutations in the RBD that would change the ability of the virus to bind ACE2 and/or for RBD-directed antibodies to strike their targets.
In their new study, published in the journal Science Translational Medicine, Bloom, Greaney, and colleagues looked again to the thousands of possible RBD variants to understand how antibodies might be expected to hit their targets there . This time, they wanted to explore any differences between RBD-directed antibodies based on how they were acquired.
Again, they turned to deep mutational scanning. First, they created libraries of all 3,800 possible RBD single amino acid mutants and exposed the libraries to samples taken from vaccinated individuals and unvaccinated individuals who’d been previously infected. All vaccinated individuals had received two doses of the Moderna mRNA vaccine. This vaccine works by prompting a person’s cells to produce the spike protein, thereby launching an immune response and the production of antibodies.
By closely examining the results, the researchers uncovered important differences between acquired immunity in people who’d been vaccinated and unvaccinated people who’d been previously infected with SARS-CoV-2. Specifically, antibodies elicited by the mRNA vaccine were more focused to the RBD compared to antibodies elicited by an infection, which more often targeted other portions of the spike protein. Importantly, the vaccine-elicited antibodies targeted a broader range of places on the RBD than those elicited by natural infection.
These findings suggest that natural immunity and vaccine-generated immunity to SARS-CoV-2 will differ in how they recognize new viral variants. What’s more, antibodies acquired with the help of a vaccine may be more likely to target new SARS-CoV-2 variants potently, even when the variants carry new mutations in the RBD.
It’s not entirely clear why these differences in vaccine- and infection-elicited antibody responses exist. In both cases, RBD-directed antibodies are acquired from the immune system’s recognition and response to viral spike proteins. The Seattle team suggests these differences may arise because the vaccine presents the viral protein in slightly different conformations.
Also, it’s possible that mRNA delivery may change the way antigens are presented to the immune system, leading to differences in the antibodies that get produced. A third difference is that natural infection only exposes the body to the virus in the respiratory tract (unless the illness is very severe), while the vaccine is delivered to muscle, where the immune system may have an even better chance of seeing it and responding vigorously.
Whatever the underlying reasons turn out to be, it’s important to consider that humans are routinely infected and re-infected with other common coronaviruses, which are responsible for the common cold. It’s not at all unusual to catch a cold from seasonal coronaviruses year after year. That’s at least in part because those viruses tend to evolve to escape acquired immunity, much as SARS-CoV-2 is now in the process of doing.
The good news so far is that, unlike the situation for the common cold, we have now developed multiple COVID-19 vaccines. The evidence continues to suggest that acquired immunity from vaccines still offers substantial protection against the new variants now circulating around the globe.
The hope is that acquired immunity from the vaccines will indeed produce long-lasting protection against SARS-CoV-2 and bring an end to the pandemic. These new findings point encouragingly in that direction. They also serve as an important reminder to roll up your sleeve for the vaccine if you haven’t already done so, whether or not you’ve had COVID-19. Our best hope of winning this contest with the virus is to get as many people immunized now as possible. That will save lives, and reduce the likelihood of even more variants appearing that might evade protection from the current vaccines.
 Antibodies elicited by mRNA-1273 vaccination bind more broadly to the receptor binding domain than do those from SARS-CoV-2 infection. Greaney AJ, Loes AN, Gentles LE, Crawford KHD, Starr TN, Malone KD, Chu HY, Bloom JD. Sci Transl Med. 2021 Jun 8.
COVID-19 Research (NIH)
Bloom Lab (Fred Hutchinson Cancer Research Center, Seattle)
NIH Support: National Institute of Allergy and Infectious Diseases
Posted on by Dr. Francis Collins
More than 170 million Americans already have received COVID-19 vaccines. As this number continues to grow and expand to younger age groups, I’m filled with overwhelming gratitude for all of the researchers who worked so diligently, over the course of decades, to build the scientific foundation for these life-saving vaccines. One of them is Dr. Kizzmekia Corbett, who played a central role in the fact that, in the span of less than a year, we were able to develop safe and effective mRNA-based vaccines to protect against this devastating infectious disease.
As leader of the immunopathogenesis team at NIH’s Dale and Betty Bumpers Vaccine Research Center in Bethesda, MD, Dr. Corbett was ready, willing, and able when the COVID-19 pandemic emerged to take the critical first steps in developing what would become the Moderna and Pfizer/BioNTech mRNA vaccines. Recently, she accepted a position at Harvard University T.H. Chan School of Public Health, Boston, where she will soon open her own viral immunology lab to help inform future vaccine development for coronaviruses and other respiratory viruses.
While she was preparing for her move to Harvard, I had a chance to speak with Dr. Corbett about her COVID-19 research experience and what it was like to get immunized with the vaccine that she helped to create. Our conversation was part of an NIH Facebook Live event in which we connected virtually from our homes in Maryland. Here is a condensed version of our chat.
Collins: You’ve studied SARS, MERS, and other coronaviruses for many years. Then, in early January 2020, like all of us, you heard that something was going on that sounded worrisome in Wuhan, China. What did you think?
Corbett: Well, the story actually began for me on December 31, 2019. My boss Dr. Barney Graham sent me an email at 6 a.m. that said: “Get ready for 2020.” There had been some news of a respiratory virus outbreak in the Wuhan district of China. I honestly wrote it off as probably a strain of the flu. Then, we got back to NIH after the holidays, and it was determined around January 6 that the virus was for certain a coronavirus. That meant our team would be responding to it.
We sat down and planned to monitor the situation very closely. We knew exactly what to do, based on our past work. We would go into full force to make a vaccine—the one now known as “the Moderna vaccine” —as quickly as possible for testing in a clinical trial. The goal was to make the vaccine in 100 days. And so when the genetic sequence of this new virus came out on January 10, I sprung out of bed and so did everyone on the team. It’s been kind of a whirlwind ever since.
Collins: Tell us a little bit more about that. The sequence got posted on the internet by a Chinese scientist. So you have this sequence, and everyone gathers in NIH’s Vaccine Research Center. Then what happens?
Corbett: The cool thing about this type of technology is you don’t even need the lab to design the vaccine. All you need are the letters, or sequence, that encodes the virus’ genetic material displayed on your computer screen. We could actually do the work from our homes, obviously in close conversation with each other.
This sequence is the virus’s genetic code. Just like humans have families—brothers, sisters, cousins—viruses also have families. So, we could see when looking at the sequence of letters, how similar this particular virus was to viruses that we’ve worked with before in the coronavirus family. It was almost like “A-ha! This is the part of the sequence that represents the protein on the surface of the virus.”
We knew that we could take the sequence of that surface protein and use all of the knowledge that we had from previous years to design a vaccine. And that’s what we did. We took that sequence on our computer screen and said we said this is exactly how we want this vaccine to look. The process was as straightforward as that.
Collins: In other words, you already knew that these coronaviruses have spike proteins on their surface and that’s the thing that’s going to be really useful for making an antibody. You’d already taken this approach in developing a vaccine for MERS, right?
Corbett: Exactly, we’d done that for MERS. Vaccines are basically a way to teach your body how to see a pathogen. Over the years, as vaccinology and technology have progressed, different scientists have figured out that you don’t really need the whole virus as a part of the vaccine. You can just take a small portion of that virus to alert your body.
In this case, taking the spike protein and teaching your immune system how to specifically spot and attack it, you can now protect yourself from COVID-19. So, we used the sequence of that spike protein, with some modifications to make it much better as a vaccine. We then deliver that to you as a message—messenger RNA (mRNA) —to get your muscle cells briefly to make the spike protein. Then, your body sees that spike protein hanging out on your cells and makes a really specific immune response to it. That way the next time your body sees the spike protein, if you ever come into contact with the virus, your immune system is armed and ready to attack.
Collins: Say more about this messenger RNA approach. It’s been so revolutionary and one of the reasons that we got vaccines into people’s arms in just 11 months. Had this approach ever been used before?
Corbett: Yes, messenger RNA technologies have been in development from a basic science perspective for over 15 years. A lot of that work was funded by NIH. Soon after I got to NIH, I attended a meeting in London called Transforming Vaccinology. At the time, Moderna was a smaller company that was working to make messenger RNA technologies, mostly centered around cancer therapies. But they had started to test some flu vaccines that used messenger RNA. My question to the presenter was: “Every single time I see you guys present, it looks like mRNA technology has always worked. Can you tell me a time that it hasn’t?” And he said, “I can’t.”
So, our understanding of how this technology works to make really good vaccines predates this pandemic. I think one of the worries that many people have is how fast and how new this technology is. But all science is compounded knowledge—everything builds on itself.
Collins: Right! We only learned about messenger RNA, because back in the 1950s and 1960s, some researchers decided to figure out how the information in our genetic instruction book, our DNA, can ultimately turn into proteins. It turned out that the message that carries that information is made of RNA.
So, you knew which kinds of letters to program into the messenger RNA vaccine. Would you explain how this vaccine, its messenger RNA, produces a spike protein. Where does that step happen?
Corbett: Your cells are machines built for this kind of thing. I like to remind people that, on a day-in, day-out basis, our cells make proteins—all of the hormones and other things our bodies needs to survive. So, we’re not teaching the cells to do anything different than they would normally do. That’s important to understand.
The way that cells do this is by reading the mRNA sequence. As they’re reading that sequence, they chew it up, like eating it, and say, “Okay, this sequence is for this very specific protein.” Then, they make that protein and push it to the surface of your cells. That’s how it happens.
Collins: And for mRNA vaccines, that’s the point when your immune system says “Wait a minute! I don’t recognize that as part of me, so I’ve got to make an antibody to it.” Then you’re off to the races and develop your immunity. Now that this mRNA vaccine strategy has succeeded for COVID-19, could it be applied to other infectious diseases or even non-infectious conditions?
Corbett: Yes, I heard that about 60 new companies have sprouted up in the last year around messenger RNA technology. They have ideas for different types of infectious disease vaccines and cancer therapies. I expect that this technology will be transformative to medicine in general.
Collins: Here’s a question from social media: “Why does it take two shots for the Pfizer and the Moderna mRNA vaccines? Why isn’t one good enough?”
Corbett: The way that these vaccines work is much like an alarm clock. Imagine your immune system is in bed and the first shot is the alarm clock going off to say, “Hey, wake up and get ready.” And just like I did this morning, the immune system pressed snooze and took a little nap. But when you hear the alarm clock the second time, it’s like someone rushing into your room and pouring a cold bucket of water on you. You have no choice but to get out of bed.
That’s what the second dose of the vaccine does. It pushes your immune response to the next level. That’s why you need two shots to get the type of efficacy that you want and be fully protected for the optimal immune response.
Collins: You were a co-leader of the team that created what became the Moderna vaccine—and you ended up getting immunized with the Moderna vaccine. What did that feel like?
Corbett: It was pretty surreal. I cried. At the end of it, I felt a lot of relief after getting my vaccine, particularly after getting the second dose. There was this breath of fresh air. It was also a birthday present. I got my second dose the day before my 35th birthday, as a birthday present to myself.
Collins: I have to admit, I cried a little bit too after my second dose. It’s just the sense of relief and incredible gratitude that we’ve reached this point. Here we are with vaccines that have 95 percent effectiveness and an incredibly good safety record, which is almost better than we could have hoped for. I’m a person of faith, so there were a lot of my prayers that went into this and it sure felt like they got answered.
Corbett: Yes, same.
Collins: You are out there a lot talking to people about the vaccines. There are still about 100 million Americans that have not yet received their first dose. Many of them still unsure about getting vaccinated. What do you say to those who are on the fence?
Corbett: In this past year, I’ve spent a lot of time talking about the vaccine with people in the community. One thing that I realized, is that I don’t need to say anything unless I’m asked. I think it’s important that I listen first, instead of just speaking.
So I do that, and I try to answer people’s inquiries as specifically as possible. But people have some very broad questions. One thing that is happening is people are seeing vaccines being developed right before their eyes. That can be a little confusing. I try to explain the process, how we went from the preclinical stage all the way to the point of getting the vaccine to hundreds of millions of people. I explain how each step along the way is very highly vetted by regulatory agencies and data safety monitoring committees. I also tell them that the monitoring continues. People from the clinical trials are still being evaluated, and there’s monitoring in the real world as the vaccine is being rolled out. I think that all of those things are really important for people to know.
Collins: Another question from social media: “As a successful scientist, what advice would you give to people who are thinking about a career in science?”
Corbett: If you think you’re interested, you just have to start. There are internship programs, there are scholarship programs, there are shadowing programs all over this country and even globally that can help you get your feet wet. I think the first thing that you want to do with any career is to figure out whether or not you like it. The only way that you can do that is to just explore, explore, explore.
Collins: Didn’t you kind of roll up your sleeves and take the plunge at a young age?
Corbett: Yes, at age 16, I went off and did summer internships at the University of North Carolina. I was able to see first-hand the day-to-day life of science and what being a scientist would look like. That was really important for me. That’s what I mean by exploring.
Collins: And a follow-up question: “Is the biomedical research community welcoming to women of color?”
Corbett: Not always, frankly. I was very fortunate to have been under the wings of a lot of mentors and advocates, who have helped to advance my career to where it is now. I had great mentors at NIH. My graduate school mentor was amazing, and my main collaborator in the coronavirus field was on my dissertation committee. Even prior to this pandemic, when I was doing work that was very obscure, he checked on me very often and made sure that he had a sense of where I wanted to go and how he could help me get there, including collaborating with me.
That kind of thing is very important, particularly for women of color or anyone from a marginalized community. That’s because there will be a point where there might be a glass ceiling. Unfortunately, we don’t necessarily have the tools to break those just yet. So, someone else is going to have to break those down, and most often than not, that person is going to have to be a white man. Finding those people who are allies with you and joining in your fight for your career trajectory is very helpful.
I remember when I was choosing a college, it was a very difficult decision for me. I got accepted into Ivy League schools, and I’d gone to all of the scholarship weekends all over the country. When I was making the decision, my dad said, “Kizzy, just always go where there is love.”
That really sticks to me with every single choice that I make around my career. You want to be at a place that’s welcoming, a place that understands you, and a place that fosters the next version of who you are destined to be. You need to make sure to step back outside of the day-to-day stuff and say, “Okay, does this place love me and people like me?” It’s important to remember that’s how you thrive: when you are comfortable in and in love with your environment.
Collins: Yes, we have to move our scientific workforce into a place where it is not necessary for a white man to advocate for a talented Black woman. There’s something very wrong with that particular circumstance. As NIH Director, I want to assure you, we are motivated more than ever to change that, including through a new initiative called UNITE. We’re missing out on welcoming the talents of so many folks who currently don’t see our research agenda as theirs, and we need to change that.
Kizzmekia, this has been a lot of fun. Thank you for giving us a half-hour of your time when you’re in the midst of this crazy two-week period of moving from Bethesda to Boston. We wish you the very best for this next chapter, which I know is going to be just amazing.
Corbett: Thank you so much.
Video: COVID-19 mRNA Vaccine Q & A – Kizzmekia Corbett and Francis Collins (NIH)
Video: Lead COVID-19 scientist Kizzmekia Corbett to join Harvard Chan School faculty (Harvard University, Boston)
COVID-19 Research (NIH)
Dale and Betty Bumpers Vaccine Research Center (National Institute of Allergy and Infectious Diseases/NIH)
UNITE Initiative (NIH)
Posted on by Dr. Francis Collins
Clinical trials have shown the COVID-19 vaccines now being administered around the country are highly effective in protecting fully vaccinated individuals from the coronavirus SARS-CoV-2. But will they continue to offer sufficient protection as the frequency of more transmissible and, in some cases, deadly emerging variants rise?
More study and time is needed to fully answer this question. But new data from Israel offers an early look at how the Pfizer/BioNTech vaccine is holding up in the real world against coronavirus “variants of concern,” including the B.1.1.7 “U.K. variant” and the B.1.351 “South African variant.” And, while there is some evidence of breakthrough infections, the findings overall are encouraging.
Israel was an obvious place to look for answers to breakthrough infections. By last March, more than 80 percent of the country’s vaccine-eligible population had received at least one dose of the Pfizer/BioNTech vaccine. An earlier study in Israel showed that the vaccine offered 94 percent to 96 percent protection against infection across age groups, comparable to the results of clinical trials. But it didn’t dig into any important differences in infection rates with newly emerging variants, post-vaccination.
To dig a little deeper into this possibility, a team led by Adi Stern, Tel Aviv University, and Shay Ben-Shachar, Clalit Research Institute, Tel Aviv, looked for evidence of breakthrough infections in several hundred people who’d had at least one dose of the Pfizer/BioNTech vaccine . The idea was, if this vaccine were less effective in protecting against new variants of concern, the proportion of infections caused by them should be higher in vaccinated compared to unvaccinated individuals.
During the study, reported as a pre-print in MedRxiv, it became clear that B.1.1.7 was the predominant SARS-CoV-2 variant in Israel, with its frequency increasing over time. By comparison, the B.1.351 “South African” variant was rare, accounting for less than 1 percent of cases sampled in the study. No other variants of concern, as defined by the World Health Organization, were detected.
In total, the researchers sequenced SARS-CoV-2 from more than 800 samples, including vaccinated individuals and matched unvaccinated individuals with similar characteristics including age, sex, and geographic location. They identified nearly 250 instances in which an individual became infected with SARS-CoV-2 after receiving their first vaccine dose, meaning that they were only partially protected. Almost 150 got infected sometime after receiving the second dose.
Interestingly, the evidence showed that these breakthrough infections with the B.1.1.7 variant occurred slightly more often in people after the first vaccine dose compared to unvaccinated people. No evidence was found for increased breakthrough rates of B.1.1.7 a week or more after the second dose. In contrast, after the second vaccine dose, infection with the B.1.351 became slightly more frequent. The findings show that people remain susceptible to B.1.1.7 following a single dose of vaccine. They also suggest that the two-dose vaccine may be slightly less effective against B.1.351 compared to the original or B.1.1.7 variants.
It’s important to note, however, that the researchers only observed 11 infections with the B.1.351 variant—eight of them in individuals vaccinated with two doses. Interestingly, all eight tested positive seven to 13 days after receiving their second dose. No one in the study tested positive for this variant two weeks or more after the second dose.
Many questions remain, including whether the vaccines reduced the duration and/or severity of infections. Nevertheless, the findings are a reminder that—while these vaccines offer remarkable protection—they are not foolproof. Breakthrough infections can and do occur.
In fact, in a recent report in the New England Journal of Medicine, NIH-supported researchers detailed the experiences of two fully vaccinated individuals in New York who tested positive for COVID-19 . Though both recovered quickly at home, genomic data in those cases revealed multiple mutations in both viral samples, including a variant first identified in South Africa and Brazil, and another, which has been spreading in New York since November.
These findings in Israel and the United States also highlight the importance of tracking coronavirus variants and making sure that all eligible individuals get fully vaccinated as soon as they have the opportunity. They show that COVID-19 testing will continue to play an important role, even in those who’ve already been vaccinated. This is even more important now as new variants continue to rise in frequency.
Just over 100 million Americans aged 18 and older—about 40 percent of adults—are now fully vaccinated . However, we need to get that number much higher. If you or a loved one haven’t yet been vaccinated, please consider doing so. It will help to save lives and bring this pandemic to an end.
 Evidence for increased breakthrough rates of SARS-CoV-2 variants of concern in BNT162b2 mRNA vaccinated individuals. Kustin T et al. medRxiv. April 16, 2021.
 Vaccine breakthrough infections with SARS-CoV-2 variants. Hacisuleyman E, Hale C, Saito Y, Blachere NE, Bergh M, Conlon EG, Schaefer-Babajew DJ, DaSilva J, Muecksch F, Gaebler C, Lifton R, Nussenzweig MC, Hatziioannou T, Bieniasz PD, Darnell RB. N Engl J Med. 2021 Apr 21.
 COVID-19 vaccinations in the United States. Centers for Disease Control and Prevention.
COVID-19 Research (NIH)
Stern Lab (Tel Aviv University, Israel)
Ben-Shachar Lab (Clalit Research Institute, Tel Aviv, Israel)
NIH Support: National Institute of Allergy and Infectious Diseases
Posted on by Dr. Francis Collins
There are many reasons to be excited about the three COVID-19 vaccines that are now getting into arms across the United States. At the top of the list is their extremely high level of safety and protection against SARS-CoV-2, the coronavirus that causes COVID-19. Of course, those data come from clinical trials that were rigorously conducted under optimal research conditions. One might wonder how well those impressive clinical trial results will translate to the real world.
A new study published in the New England Journal of Medicine  offers an early answer for the Pfizer/BioNTech vaccine. The Pfizer product is an mRNA vaccine that was found in a large clinical trial to be up to 95 percent effective in preventing COVID-19, leading to its Emergency Use Authorization last December.
The new data, which come from Israel, are really encouraging. Based on a detailed analysis of nearly 600,000 people vaccinated in that nation, a research team led by Ran Balicer, The Clalit Research Institute, Tel Aviv, found that the risk of symptomatic COVID-19 infection dropped by 94 percent a week after individuals had received both doses of the Pfizer vaccine. That’s essentially the same very high level of protection that was seen in the data gathered in the earlier U.S. clinical trial.
The study also found that just a single shot of the two-dose vaccine led to a 57 percent drop in the incidence of symptomatic COVID-19 infections and a 62 percent decline in the risk of severe illness after two to three weeks. Note, however, that the protection clearly got better after folks received the second dose. While it’s too soon to say how many lives were saved in Israel thanks to full vaccination, the early data not surprisingly suggest a substantial reduction in mortality.
Israel, which is about as large as New Jersey with a population of around 9 million, currently has the world’s highest COVID-19 vaccination rate. In addition to its relatively small size, Israel also has a national health system and one of the world’s largest integrated health record databases, making it a natural choice to see how well one of the new vaccines was working in the real world.
The study took place from December 20, 2020, the start of Israel’s first vaccination drive, through February 1, 2021. This also coincided with Israel’s third and largest wave of COVID-19 infections and illness. During this same period, the B.1.1.7 variant, which was first detected in the United Kingdom, gradually became Israel’s dominant strain. That’s notable because the U.K. variant spreads from person-to-person more readily and may be associated with an increased risk of death compared with other variants .
Balicer and his colleagues reviewed data on 596,618 fully vaccinated individuals, ages 16 and older. A little less than one third—about 170,000—of the people studied were over age 60. To see how well the vaccine worked, the researchers carefully matched each of the vaccinated individuals in the study to an unvaccinated person with similar demographics as well as risks of infection, severe illness, and other important health attributes.
The results showed that the vaccine works remarkably well. In fact, the researchers determined that the Pfizer/BioNTech vaccine is similarly effective—94 percent to 96 percent—across adults in different age groups. It also appears that the vaccine works about equally well for individuals age 70 and older as it does for younger people.
So far, more than 92 million total vaccine doses have been administered in the U.S. With the Janssen COVID-19 vaccine (also called the Johnson & Johnson vaccine) now coming online, that number will rise even faster. For those of you who haven’t had the opportunity just yet, these latest findings should come as added encouragement to roll up your sleeve for any one of the authorized vaccines as soon as your invitation arrives.
 BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting. Dagan N, Barda N, Kepten E, Miron O, Perchik S, Katz MA, Hernán MA, Lipsitch M, Reis B, Balicer RD. N Engl J Med. 2021 Feb 24.
 Emerging SARS-CoV-2 Variants. Centers for Disease Control and Prevention.
COVID-19 Research (NIH)
Clalit Research Institute (Tel Aviv, Israel)
Ran Balicer (Clalit Research Institute)
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