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acquired immunity

How Immunity Generated from COVID-19 Vaccines Differs from an Infection

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Orginal viral spike is shown binding to antibody from vaccine and from infection. Variant spikes only bind to antibody from vaccine.

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 [1]. 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.

Reference:

[1] 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.

Links:

COVID-19 Research (NIH)

Bloom Lab (Fred Hutchinson Cancer Research Center, Seattle)

NIH Support: National Institute of Allergy and Infectious Diseases


An Evolutionary Guide to New Immunotherapies

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Credit: Dave Titensor, University of Utah, Salt Lake City

One of the best ways to learn how something works is to understand how it’s built. How it came to be. That’s true not only if you play a guitar or repair motorcycle engines, but also if you study the biological systems that make life possible. Evolutionary studies, comparing the development of these systems across animals and organisms, are now leading to many unexpected biological discoveries and promising possibilities for preventing and treating human disease.

While there are many evolutionary questions to ask, Brenda Bass, a distinguished biochemist at University of Utah, Salt Lake City, has set her sights on a particularly profound one: How has innate immunity evolved through the millennia in all living things, including humans? Innate immunity is the immune system’s frontline defense, the first responders that take control of an emerging infectious situation and, if needed, signal for backup.

Exploring the millennia for clues about innate immunity takes a special team, and Bass has assembled a talented one. It includes her Utah colleague Nels Elde, a geneticist; immunologist Dan Stetson, University of Washington, Seattle; and biochemist Jane Jackman, Ohio State University, Columbus.

With a 2020 NIH Director’s Transformative Research Award, this hard-working team will embark on studies looking back at 450 million years of evolution: the point in time when animals diverged to develop very distinct methods of innate immune defense [1]. The team members hope to uncover new possibilities encoded in the innate immune system, especially those that might be latent but still workable. The researchers will then explore whether their finds can be repurposed not only to boost our body’s natural response to external threats but also to internal threats like cancer.

Bass brings a unique perspective to the project. As a postdoc in the 1980s, she stumbled upon a whole new class of enzymes, called ADARs, that edit RNA [2]. Their function was mysterious at the time. It turns out that ADARs specifically edit a molecule called double-stranded RNA (dsRNA). When viruses infect cells in animals, including humans, they make dsRNA, which the innate immune system detects as a sign that a cell has been invaded.

It also turns out that animal cells make their own dsRNA. Over the years, Bass and her lab have identified thousands of dsRNAs made in animal cells—in fact, a significant number of human genes produce dsRNA [3]. Also interesting, ADARs are crucial to marking our own dsRNA as “self” to avoid triggering an immune response when we don’t need it [4].

Bass and others have found that evolution has produced dramatic differences in the biochemical pathways powering the innate immune system. In vertebrate animals, dsRNA leads to release of the immune chemical interferon, a signaling pathway that invertebrate species don’t have. Instead, in response to detecting dsRNA from an invader, and repelling it, worms and other invertebrates trigger a gene-silencing pathway known as RNA interference, or RNAi.

With the new funding, Bass and team plan to mix and match immune strategies from simple and advanced species, across evolutionary time, to craft an entirely new set of immune tools to fight disease. The team will also build new types of targeted immunotherapies based on the principles of innate immunity. Current immunotherapies, which harness a person’s own immune system to fight disease, target infections, autoimmune disorders, and cancer. But they work through our second-line adaptive immune response, which is a biological system unique to vertebrates.

Bass and her team will first hunt for more molecules like ADARs: innate immune checkpoints, as they refer to them. The name comes from a functional resemblance to the better-known adaptive immune checkpoints PD-1 and CTLA-4, which sparked a revolution in cancer immunotherapy. The team will run several screens that sort molecules successful at activating innate immune responses—both in invertebrates and in mammals—hoping to identify a range of durable new immune switches that evolution skipped over but that might be repurposed today.

Another intriguing direction for this research stems from the observation that decreasing normal levels of ADARs in tumors kickstarts innate immune responses that kill cancer cells [5]. Along these lines, the scientists plan to test newly identified immune switches to look for novel ways to fight cancer where existing approaches have not worked.

Evolution is the founding principle for all of biology—organisms learn from what works to improve their ability to survive. In this case, research to re-examine such lessons and apply them for new uses may help transform bygone evolution into a therapeutic revolution!

References:

[1] Evolution of adaptive immunity from transposable elements combined with innate immune systems. Koonin EV, Krupovic M. Nat Rev Genet. 2015 Mar;16(3):184-192.

[2] A developmentally regulated activity that unwinds RNA duplexes. Bass BL, Weintraub H. Cell. 1987 Feb 27;48(4):607-613.

[3] Mapping the dsRNA World. Reich DP, Bass BL. Cold Spring Harb Perspect Biol. 2019 Mar 1;11(3):a035352.

[4] To protect and modify double-stranded RNA – the critical roles of ADARs in development, immunity and oncogenesis. Erdmann EA, Mahapatra A, Mukherjee P, Yang B, Hundley HA. Crit Rev Biochem Mol Biol. 2021 Feb;56(1):54-87.

[5] Loss of ADAR1 in tumours overcomes resistance to immune checkpoint blockade. Ishizuka JJ, Manguso RT, Cheruiyot CK, Bi K, Panda A, et al. Nature. 2019 Jan;565(7737):43-48.

Links:

Bass Lab (University of Utah, Salt Lake City)

Elde Lab (University of Utah)

Jackman Lab (Ohio State University, Columbus)

Stetson Lab (University of Washington, Seattle)

Bass/Elde/Jackman/Stetson Project Information (NIH RePORTER)

NIH Director’s Transformative Research Award Program (Common Fund)

NIH Support: Common Fund; National Cancer Institute


Study of Healthcare Workers Shows COVID-19 Immunity Lasts Many Months

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Healthcare Workers
Credit: iStock/SelectStock

Throughout the COVID-19 pandemic, healthcare workers around the world have shown willingness to put their own lives on the line for their patients and communities. Unfortunately, many have also contracted SARS-CoV-2, the coronavirus that causes of COVID-19, while caring for patients. That makes these frontline heroes helpful in another way in the fight against SARS-CoV-2: determining whether people who have recovered from COVID-19 can be reinfected by the virus.

New findings from a study of thousands of healthcare workers in England show that those who got COVID-19 and produced antibodies against the virus are highly unlikely to become infected again, at least over the several months that the study was conducted. In the rare instances in which someone with acquired immunity for SARS-CoV-2 subsequently tested positive for the virus within a six month period, they never showed any signs of being ill.

Some earlier studies have shown that people who survive a COVID-19 infection continue to produce protective antibodies against key parts of the virus for several months. But how long those antibodies last and whether they are enough to protect against reinfection have remained open questions.

In search of answers, researchers led by David Eyre, University of Oxford, England, looked to more than 12,000 healthcare workers at Oxford University Hospitals from April to November 2020. At the start of the study, 11,052 of them tested negative for antibodies against SARS-CoV-2, suggesting they hadn’t had COVID-19. But the other 1,246 tested positive for antibodies, evidence that they’d already been infected.

After this initial testing, all participants received antibody tests once every two months and diagnostic tests for an active COVID-19 infection at least every other week. What the researchers discovered was rather interesting. Eighty-nine of the 11,052 healthcare workers who tested negative at the outset later got a symptomatic COVID-19 infection. Another 76 individuals who originally tested negative for antibodies tested positive for COVID-19, despite having no symptoms.

Here’s the good news: Just three of these more than 1400 antibody-positive individuals subsequently tested positive for SARS-CoV-2. What’s more, not one of them had any symptoms of COVID-19.

The findings, which were posted as a pre-print on medRxiv, suggest that acquired immunity from an initial COVID-19 infection offers protection against reinfection for six months or maybe longer. Questions remain about whether the acquired immunity is due to the observed antibodies alone or their interplay with other immune cells. It will be important to continue to follow these healthcare workers even longer, to learn just how long their immune protection might last.

Meanwhile, more than 15 million people in the United States have now tested positive for COVID-19, leading to more than 285,000 deaths. Last week, the U.S. reported for the first time more than 200,000 new infections, with hospitalizations and deaths also on the rise.

While the new findings on reinfection come as good news to be sure, it’s important to remember that the vast majority of the 328 million Americans still remain susceptible to this life-threatening virus. So, throughout this holiday season and beyond—as we eagerly await the approval and widespread distribution of vaccines—we must all continue to do absolutely everything we can to protect ourselves, our loved ones, and our communities from COVID-19.

Reference:

[1] Antibodies to SARS-CoV-2 are associated with protection against reinfection. Lumley, S.F. et al. MedRxiv. 19 November 2020.

Links:

Coronavirus (COVID) (NIH)

Combat COVID (U.S. Department of Health and Human Services, Washington, D.C.)

David Eyre (University of Oxford, England)


Two Studies Show COVID-19 Antibodies Persist for Months

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Antibodies against SARS-CoV-2
Caption: Artistic rendering of SARS-CoV-2 virus (orange) covered with antibodies (white), generated by an immune B cell (gray) at the bottom left. Credit: iStock/selvanegra

More than 8 million people in the United States have now tested positive for COVID-19. For those who’ve recovered, many wonder if fending off SARS-CoV-2—the coronavirus that causes COVID-19—one time means their immune systems will protect them from reinfection. And, if so, how long will this “acquired immunity” last?

The early data brought hope that acquired immunity was possible. But some subsequent studies have suggested that immune protection might be short-lived. Though more research is needed, the results of two recent studies, published in the journal Science Immunology, support the early data and provide greater insight into the nature of the human immune response to this coronavirus [1,2].

The new findings show that people who survive a COVID-19 infection continue to produce protective antibodies against key parts of the virus for at least three to four months after developing their first symptoms. In contrast, some other antibody types decline more quickly. The findings offer hope that people infected with the virus will have some lasting antibody protection against re-infection, though for how long still remains to be determined.

In one of the two studies, partly funded by NIH, researchers led by Richelle Charles, Massachusetts General Hospital, Boston, sought a more detailed understanding of antibody responses following infection with SARS-CoV-2. To get a closer look, they enrolled 343 patients, most of whom had severe COVID-19 requiring hospitalization. They examined their antibody responses for up to 122 days after symptoms developed and compared them to antibodies in more than 1,500 blood samples collected before the pandemic began.

The researchers characterized the development of three types of antibodies in the blood samples. The first type was immunoglobulin G (IgG), which has the potential to confer sustained immunity. The second type was immunoglobulin A (IgA), which protects against infection on the body’s mucosal surfaces, such as those found in the respiratory and gastrointestinal tracts, and are found in high levels in tears, mucus, and other bodily secretions. The third type is immunoglobulin M (IgM), which the body produces first when fighting an infection.

They found that all three types were present by about 12 days after infection. IgA and IgM antibodies were short-lived against the spike protein that crowns SARS-CoV-2, vanishing within about two months.

The good news is that the longer-lasting IgG antibodies persisted in these same patients for up to four months, which is as long as the researchers were able to look. Levels of those IgG antibodies also served as an indicator for the presence of protective antibodies capable of neutralizing SARS-CoV-2 in the lab. Even better, that ability didn’t decline in the 75 days after the onset of symptoms. While longer-term study is needed, the findings lend support to evidence that protective antibody responses against the novel virus do persist.

The other study came to very similar conclusions. The team, led by Jennifer Gommerman and Anne-Claude Gingras, University of Toronto, Canada, profiled the same three types of antibody responses against the SARS-CoV-2 spike protein, They created the profiles using both blood and saliva taken from 439 people, not all of whom required hospitalization, who had developed COVID-19 symptoms from 3 to 115 days prior. The team then compared antibody profiles of the COVID-19 patients to those of people negative for COVID-19.

The researchers found that the antibodies against SARS-CoV-2 were readily detected in blood and saliva. IgG levels peaked about two weeks to one month after infection, and then remained stable for more than three months. Similar to the Boston team, the Canadian group saw IgA and IgM antibody levels drop rapidly.

The findings suggest that antibody tests can serve as an important tool for tracking the spread of SARS-CoV-2 through our communities. Unlike tests for the virus itself, antibody tests provide a means to detect infections that occurred sometime in the past, including those that may have been asymptomatic. The findings from the Canadian team further suggest that tests of IgG antibodies in saliva may be a convenient way to track a person’s acquired immunity to COVID-19.

Because IgA and IgM antibodies decline more quickly, testing for these different antibody types also could help to distinguish between an infection within the last two months and one that more likely occurred even earlier. Such details are important for filling in gaps in our understanding COVID-19 infections and tracking their spread in our communities.

Still, there are rare reports of individuals who survived one bout with COVID-19 and were infected with a different SARS-CoV-2 strain a few weeks later [3]. The infrequency of such reports, however, suggests that acquired immunity after SARS-CoV-2 infection is generally protective.

There remain many open questions, and answering them will require conducting larger studies with greater diversity of COVID-19 survivors. So, I’m pleased to note that the NIH’s National Cancer Institute (NCI) recently launched the NCI Serological Sciences Network for COVID19 (SeroNet), now the nation’s largest coordinated effort to characterize the immune response to COVID-19 [4].

The network was established using funds from an emergency Congressional appropriation of more than $300 million to develop, validate, improve, and implement antibody testing for COVID-19 and related technologies. With help from this network and ongoing research around the world, a clearer picture will emerge of acquired immunity that will help to control future outbreaks of COVID-19.

References:

[1] Persistence and decay of human antibody responses to the receptor binding domain of SARS-CoV-2 spike protein in COVID-19 patients. Iyer AS, Jones FK, Nodoushani A, Ryan ET, Harris JB, Charles RC, et al. Sci Immunol. 2020 Oct 8;5(52):eabe0367.

[2] Persistence of serum and saliva antibody responses to SARS-CoV-2 spike antigens in COVID-19 patients. Isho B, Abe KT, Zuo M, Durocher Y, McGeer AJ, Gommerman JL, Gingras AC, et al. Sci Immunol. 2020 Oct 8;5(52):eabe5511.

[3] What reinfections mean for COVID-19. Iwasaki A. Lancet Infect Dis, 2020 October 12. [Epub ahead of print]

[4] NIH to launch the Serological Sciences Network for COVID-19, announce grant and contract awardees. National Institutes of Health. 2020 October 8.

Links:

Coronavirus (COVID-19) (NIH)

Charles Lab (Massachusetts General Hospital, Boston)

Gingras Lab (University of Toronto, Canada)

Jennifer Gommerman (University of Toronto, Canada)

NCI Serological Sciences Network for COVID-19 (SeroNet) (National Cancer Institute/NIH)

NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of General Medical Sciences; National Cancer Institute


Study Finds People Have Short-Lived Immunity to Seasonal Coronaviruses

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Microscopic view of Coronavirus
Caption: Artistic rendering of coronaviruses. Credit: iStock/Naeblys

A key metric in seeking to end the COVID-19 pandemic is the likely duration of acquired immunity, which is how long people infected with SARS-CoV-2, the novel coronavirus that causes COVID-19, are protected against reinfection. The hope is that acquired immunity from natural infection—or from vaccines—will be long-lasting, but data to confirm that’s indeed the case won’t be in for many months or years.

In the meantime, a useful place to look for clues is in long-term data on reinfections with other seasonal coronaviruses. Could the behavior of less life-threatening members of the coronavirus family give us some insight into what to expect from SARS-CoV-2?

A new study, published in the journal Nature Medicine, has taken exactly this approach. The researchers examined blood samples collected continuously from 10 healthy individuals since the 1980s for evidence of infections—and reinfections—with four common coronaviruses. Unfortunately, it’s not particularly encouraging news. The new data show that immunity to other coronaviruses tends to be short-lived, with reinfections happening quite often about 12 months later and, in some cases, even sooner.

Prior to the discovery of SARS-CoV-2, six coronaviruses were known to infect humans. Four are responsible for relatively benign respiratory illnesses that regularly circulate to cause the condition we recognize as the common cold. The other two are more dangerous and, fortunately, less common: SARS-CoV-1, the virus responsible for outbreaks of Severe Acute Respiratory Syndrome (SARS), which ended in 2004; and MERS-CoV, the virus that causes the now rare Middle East Respiratory Syndrome (MERS).

In the new study, a team led by Lia van der Hoek, University of Amsterdam, the Netherlands, set out to get a handle on reinfections with the four common coronaviruses: HCoV-NL63, HCoV-229E, HCoV-OC43, and HCoV-HKU1. This task isn’t as straightforward as it might sound. That’s because, like SARS-CoV-2, infections with such viruses don’t always produce symptoms that are easily tracked. So, the researchers looked instead to blood samples from 10 healthy individuals enrolled for decades in the Amsterdam Cohort Studies on HIV-1 Infection and AIDS.

To detect coronavirus reinfections, they measured increases in antibodies to a particular portion of the nucleocapsid of each coronavirus. The nucleocapsid is a protein shell that encapsulates a coronavirus’ genetic material and serves as important targets for antibodies. An increase in antibodies targeting the nucleocapsid indicated that a person was fighting a new infection with one of the four coronaviruses.

All told, the researchers examined a total of 513 blood samples collected at regular intervals—every 3 to 6 months. In those samples, the team’s analyses uncovered 3 to 17 coronavirus infections per study participant over more than 35 years. Reinfections occurred every 6 to 105 months. But reinfections happened most frequently about a year after a previous infection.

Not surprisingly, they also found that blood samples collected in the Netherlands during the summer months—June, July, August, and September—had the lowest rate of infections for all four seasonal coronaviruses, indicating a higher frequency of infections in winter in temperate countries. While it remains to be seen, it’s possible that SARS-CoV-2 ultimately may share the same seasonal pattern after the pandemic.

These findings show that annual reinfections are a common occurrence for all other common coronaviruses. That’s consistent with evidence that antibodies against SARS-CoV-2 decrease within two months of infection [2]. It also suggests that similar patterns of reinfection may emerge for SARS-CoV-2 in the coming months and years.

At least three caveats ought to be kept in mind when interpreting these data. First, the researchers tracked antibody levels but didn’t have access to information about actual illness. It’s possible that a rise in antibodies to a particular coronavirus might have provided exactly the response needed to convert a significant respiratory illness to a mild case of the sniffles or no illness at all.

Second, sustained immunity to viruses will always be disrupted if the virus is undergoing mutational changes and presenting a new set of antigens to the host; the degree to which that might have contributed to reinfections is not known. And, third, the role of cell-based immunity in fighting off coronavirus infections is likely to be significant, but wasn’t studied in this retrospective analysis.

To prepare for COVID-19 this winter, it’s essential to understand how likely a person who has recovered from the illness will be re-infected and potentially spread the virus to other people. While much more study is needed, the evidence suggests it will be prudent to proceed carefully and with caution when it comes to long-term immunity, whether achieved through naturally acquired infections or vaccination.

While we await a COVID-19 vaccine, the best way to protect yourself, your family, and your community is to take simple steps all of us can do today: maintain social distancing, wear a mask, avoid crowded indoor gatherings, and wash your hands.

References:

[1] Seasonal coronavirus protective immunity is short-lasting. Edridge AWD, Kaczorowska J, Hoste ACR, Bakker M, Klein M, Loens K, Jebbink MF, Matser A, Kinsella CM, Rueda P, Ieven M, Goossens H, Prins M, Sastre P, Deijs M, van der Hoek L. Nat Med. 2020 Sep 14. doi: 10.1038/s41591-020-1083-1. [Published online ahead of print.]

[2] Rapid decay of anti-SARS-CoV-2 antibodies in persons with mild Covid-19. Ibarrondo FJ, Fulcher JA, Goodman-Meza D, Elliott J, Hofmann C, Hausner MA, Ferbas KG, Tobin NH, Aldrovandi GM, Yang OO. N Engl J Med. 2020 Sep 10;383(11):1085-1087.

Links:

Coronavirus (COVID-19) (NIH)

Lia van der hoek (University of Amsterdam, the Netherlands)


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