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mRNA Vaccines May Pack More Persistent Punch Against COVID-19 Than Thought

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Many people, including me, have experienced a sense of gratitude and relief after receiving the new COVID-19 mRNA vaccines. But all of us are also wondering how long the vaccines will remain protective against SARS-CoV-2, the coronavirus responsible for COVID-19.

Earlier this year, clinical trials of the Moderna and Pfizer-BioNTech vaccines indicated that both immunizations appeared to protect for at least six months. Now, a study in the journal Nature provides some hopeful news that these mRNA vaccines may be protective even longer [1].

In the new study, researchers monitored key immune cells in the lymph nodes of a group of people who received both doses of the Pfizer-BioNTech mRNA vaccine. The work consistently found hallmarks of a strong, persistent immune response against SARS-CoV-2 that could be protective for years to come.

Though more research is needed, the findings add evidence that people who received mRNA COVID-19 vaccines may not need an additional “booster” shot for quite some time, unless SARS-CoV-2 evolves into new forms, or variants, that can evade this vaccine-induced immunity. That’s why it remains so critical that more Americans get vaccinated not only to protect themselves and their loved ones, but to help stop the virus’s spread in their communities and thereby reduce its ability to mutate.

The new study was conducted by an NIH-supported research team led by Jackson Turner, Jane O’Halloran, Rachel Presti, and Ali Ellebedy at Washington University School of Medicine, St. Louis. That work builds upon the group’s previous findings that people who survived COVID-19 had immune cells residing in their bone marrow for at least eight months after the infection that could recognize SARS-CoV-2 [2]. The researchers wanted to see if similar, persistent immunity existed in people who hadn’t come down with COVID-19 but who were immunized with an mRNA vaccine.

To find out, Ellebedy and team recruited 14 healthy adults who were scheduled to receive both doses of the Pfizer-BioNTech vaccine. Three weeks after their first dose of vaccine, the volunteers underwent a lymph node biopsy, primarily from nodes in the armpit. Similar biopsies were repeated at four, five, seven, and 15 weeks after the first vaccine dose.

The lymph nodes are where the human immune system establishes so-called germinal centers, which function as “training camps” that teach immature immune cells to recognize new disease threats and attack them with acquired efficiency. In this case, the “threat” is the spike protein of SARS-COV-2 encoded by the vaccine.

By the 15-week mark, all of the participants sampled continued to have active germinal centers in their lymph nodes. These centers produced an army of cells trained to remember the spike protein, along with other types of cells, including antibody-producing plasmablasts, that were locked and loaded to neutralize this key protein. In fact, Ellebedy noted that even after the study ended at 15 weeks, he and his team continued to find no signs of germinal center activity slowing down in the lymph nodes of the vaccinated volunteers.

Ellebedy said the immune response observed in his team’s study appears so robust and persistent that he thinks that it could last for years. The researcher based his assessment on the fact that germinal center reactions that persist for several months or longer usually indicate an extremely vigorous immune response that culminates in the production of large numbers of long-lasting immune cells, called memory B cells. Some memory B cells can survive for years or even decades, which gives them the capacity to respond multiple times to the same infectious agent.

This study raises some really important issues for which we still don’t have complete answers: What is the most reliable correlate of immunity from COVID-19 vaccines? Are circulating spike protein antibodies (the easiest to measure) the best indicator? Do we need to know what’s happening in the lymph nodes? What about the T cells that are responsible for cell-mediated immunity?

If you follow the news, you may have seen a bit of a dust-up in the last week on this topic. Pfizer announced the need for a booster shot has become more apparent, based on serum antibodies. Meanwhile, the Food and Drug Administration and Centers for Disease Control and Prevention said such a conclusion would be premature, since vaccine protection looks really good right now, including for the delta variant that has all of us concerned.

We’ve still got a lot more to learn about the immunity generated by the mRNA vaccines. But this study—one of the first in humans to provide direct evidence of germinal center activity after mRNA vaccination—is a good place to continue the discussion.

References:

[1] SARS-CoV-2 mRNA vaccines induce persistent human germinal centre responses. Turner JS, O’Halloran JA, Kalaidina E, Kim W, Schmitz AJ, Zhou JQ, Lei T, Thapa M, Chen RE, Case JB, Amanat F, Rauseo AM, Haile A, Xie X, Klebert MK, Suessen T, Middleton WD, Shi PY, Krammer F, Teefey SA, Diamond MS, Presti RM, Ellebedy AH. Nature. 2021 Jun 28. [Online ahead of print]

[2] SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Turner JS, Kim W, Kalaidina E, Goss CW, Rauseo AM, Schmitz AJ, Hansen L, Haile A, Klebert MK, Pusic I, O’Halloran JA, Presti RM, Ellebedy AH. Nature. 2021 May 24. [Online ahead of print]

Links:

COVID-19 Research (NIH)

Ellebedy Lab (Washington University, St. Louis)

NIH Support: National Institute of Allergy and Infectious Diseases; National Center for Advancing Translational Sciences


Studies Confirm COVID-19 mRNA Vaccines Safe, Effective for Pregnant Women

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Credit: GettyImages/bogdankosanovic

Clinical trials have shown that COVID-19 vaccines are remarkably effective in protecting those age 12 and up against infection by the coronavirus SARS-CoV-2. The expectation was that they would work just as well to protect pregnant women. But because pregnant women were excluded from the initial clinical trials, hard data on their safety and efficacy in this important group has been limited.

So, I’m pleased to report results from two new studies showing that the two COVID-19 mRNA vaccines now available in the United States appear to be completely safe for pregnant women. The women had good responses to the vaccines, producing needed levels of neutralizing antibodies and immune cells known as memory T cells, which may offer more lasting protection. The research also indicates that the vaccines might offer protection to infants born to vaccinated mothers.

In one study, published in JAMA [1], an NIH-supported team led by Dan Barouch, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, wanted to learn whether vaccines would protect mother and baby. To find out, they enrolled 103 women, aged 18 to 45, who chose to get either the Pfizer/BioNTech or Moderna mRNA vaccines from December 2020 through March 2021.

The sample included 30 pregnant women,16 women who were breastfeeding, and 57 women who were neither pregnant nor breastfeeding. Pregnant women in the study got their first dose of vaccine during any trimester, although most got their shots in the second or third trimester. Overall, the vaccine was well tolerated, although some women in each group developed a transient fever after the second vaccine dose, a common side effect in all groups that have been studied.

After vaccination, women in all groups produced antibodies against SARS-CoV-2. Importantly, those antibodies neutralized SARS-CoV-2 variants of concern. The researchers also found those antibodies in infant cord blood and breast milk, suggesting that they were passed on to afford some protection to infants early in life.

The other NIH-supported study, published in the journal Obstetrics & Gynecology, was conducted by a team led by Jeffery Goldstein, Northwestern’s Feinberg School of Medicine, Chicago [2]. To explore any possible safety concerns for pregnant women, the team took a first look for any negative effects of vaccination on the placenta, the vital organ that sustains the fetus during gestation.

The researchers detected no signs that the vaccines led to any unexpected damage to the placenta in this study, which included 84 women who received COVID-19 mRNA vaccines during pregnancy, most in the third trimester. As in the other study, the team found that vaccinated pregnant women showed a robust response to the vaccine, producing needed levels of neutralizing antibodies.

Overall, both studies show that COVID-19 mRNA vaccines are safe and effective in pregnancy, with the potential to benefit both mother and baby. Pregnant women also are more likely than women who aren’t pregnant to become severely ill should they become infected with this devastating coronavirus [3]. While pregnant women are urged to consult with their obstetrician about vaccination, growing evidence suggests that the best way for women during pregnancy or while breastfeeding to protect themselves and their families against COVID-19 is to roll up their sleeves and get either one of the mRNA vaccines now authorized for emergency use.

References:

[1] Immunogenicity of COVID-19 mRNA vaccines in pregnant and lactating women. Collier AY, McMahan K, Yu J, Tostanoski LH, Aguayo R, Ansel J, Chandrashekar A, Patel S, Apraku Bondzie E, Sellers D, Barrett J, Sanborn O, Wan H, Chang A, Anioke T, Nkolola J, Bradshaw C, Jacob-Dolan C, Feldman J, Gebre M, Borducchi EN, Liu J, Schmidt AG, Suscovich T, Linde C, Alter G, Hacker MR, Barouch DH. JAMA. 2021 May 13.

[2] Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination in pregnancy: Measures of immunity and placental histopathology. Shanes ED, Otero S, Mithal LB, Mupanomunda CA, Miller ES, Goldstein JA. Obstet Gynecol. 2021 May 11.

[3] COVID-19 vaccines while pregnant or breastfeeding. Centers for Disease Control and Prevention.

Links:

COVID-19 Research (NIH)

Barouch Laboratory (Beth Israel Deaconess Medical Center and Harvard Medical School, Boston)

Jeffery Goldstein (Northwestern University Feinberg School of Medicine, Chicago)

NIH Support: National Institute of Allergy and Infectious Diseases; National Cancer Institute, National Institute of Child Health and Human Development; National Center for Advancing Translational Sciences; National Institute of Biomedical Imaging and Bioengineering


A Real-World Look at COVID-19 Vaccines Versus New Variants

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A woman receiving a vaccine from a doctor
Credit: Getty Images/Andrey Popov

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 [1]. 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.

Graph showing percentages of virus variants. B.1.1.7 is nearly 100% by March
Caption: Changing variant frequencies during the study. Credit: Adapted from Kustin T, medRxiv, 2021

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 [2]. 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 [3]. 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.

References:

[1] 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.

[2] 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.

[3] COVID-19 vaccinations in the United States. Centers for Disease Control and Prevention.

Links:

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


Tracking the Evolution of a ‘Variant of Concern’ in Brazil

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P.1 Variant of SARS-CoV-2 in the center of standard SARS-CoV-2. Arrows move out from the variant

By last October, about three out of every four residents of Manaus, Brazil already had been infected with SARS-CoV-2, the virus that causes COVID-19 [1]. And yet, despite hopes of achieving “herd immunity” in this city of 2.2 million in the Amazon region, the virus came roaring back in late 2020 and early 2021 to cause a second wave of illness and death [2]. How is this possible?

The answer offers a lesson in viral evolution, especially when an infectious virus such as SARS-CoV-2 replicates and spreads through a population largely unchecked. In a recent study in the journal Science, researchers tied the city’s resurgence of SARS-CoV-2 to the emergence and rapid spread of a new SARS-CoV-2 “variant of concern” known as P.1 [3]. This variant carries a unique constellation of mutations that allow it not only to sneak past the human immune system and re-infect people, but also to be about twice as transmissible as earlier variants.

To understand how this is possible, consider that each time the coronavirus SARS-CoV-2 makes copies of itself in an infected person, there’s a chance a mistake will be made. Each mistake can produce a new variant that may go on to make more copies of itself. In most cases, those random errors are of little to no consequence. This is evolution in action.

But sometimes a spelling change can occur that benefits the virus. In the special case of patients with suppressed immune systems, the virus can have ample opportunity to accrue an unusually high number of mutations. Variants carrying beneficial mutations can make more copies of themselves than other variants, allowing them to build their numbers and spread to cause more infection.

At this advanced stage of the COVID-19 pandemic, such rapidly spreading new variants remain cause for serious concern. That includes variants such as B.1.351, which originated in South Africa; B.1.1.7 which emerged in the United Kingdom; and now P.1 from Manaus, Brazil.

In the new study, Nuno Faria and Samir Bhatt, Imperial College London, U.K., and Ester Cerdeira Sabino, Universidade de Sao Paulo, Brazil, and their colleagues sequenced SARS-CoV-2 genomes from 184 patient samples collected in Manaus in November and December 2020. The research was conducted under the auspices of the Brazil-UK Centre for Arbovirus Discovery, Diagnosis, Genomics and Epidemiology (CADDE), a project focused on viral genomics and epidemiology for public health.

Those genomic data revealed the P.1 variant had acquired 17 new mutations. Ten were in the spike protein, which is the segment of the virus that binds onto human cells and the target of current COVID-19 vaccines. In fact, the new work reveals that three of these spike protein mutations make it easier for the P.1 spike to bind the human ACE2 receptor, which is SARS-CoV-2’s preferred entry point.

The first P.1 variant case was detected by genomic surveillance on December 6, 2020, after which it spread rapidly. Through further evolutionary analysis, the team estimates that P.1 must have emerged, undetected for a brief time, in mid-November 2020.

To understand better how the P.1 variant led to such an explosion of new COVID-19 cases, the researchers developed a mathematical model that integrated the genomic data with mortality data. The model suggests that P.1 may be 1.7 to 2.4 times more transmissible than earlier variants. They also estimate that a person previously infected with a variant other than P.1 will have only 54 percent to 79 percent protection against a subsequent infection with P.1.

The researchers also observed an increase in mortality following the emergence of the P.1 variant. However, it’s not yet clear if that’s an indication P.1 is inherently more deadly than earlier variants. It’s possible the increased mortality is related primarily to the extra stress on the healthcare system in Manaus from treating so many people with COVID-19.

These findings are yet another reminder of the importance of genomic surveillance and international data sharing for detecting and characterizing emerging SARS-CoV-2 variants quickly. It’s worth noting that at about the same time this variant was detected in Brazil, it also was reported in four individuals who had traveled to Brazil from Japan. The P.1 variant continues to spread rapidly across Brazil. It has also been detected in more than 37 countries [4], including the United States, where it now accounts for more than 1 percent of new cases [5].

No doubt you are wondering what this means for vaccines, such as the Pfizer and Moderna mRNA vaccines, that have been used to immunize (at least one dose) over 140 million people in the United States. Here the news is encouraging. Serum from individuals who received the Pfizer vaccine had titers of neutralizing antibodies that were only slightly reduced for P.1 compared to the original SARS-CoV-2 virus [6]. Therefore, the vaccine is predicted to be highly protective. This is another example of a vaccine providing more protection than a natural infection.

The United States has made truly remarkable progress in combating COVID-19, but we must heed this lesson from Manaus: this terrible pandemic isn’t over just yet. While the P.1 variant remains at low levels here for now, the “U.K. variant” B.1.1.7 continues to spread rapidly and now is the most prevalent variant circulating in the U.S., accounting for 44 percent of new cases [6]. Fortunately, the mRNA vaccines also work well against B.1.1.7.

We must continue to do absolutely everything possible, individually and collectively, to prevent these new SARS-CoV-2 variants from slowing or even canceling the progress made over the last year. We need to remain vigilant for just a while longer, while encouraging our friends, neighbors, and loved ones to get vaccinated.

References:

[1] Three-quarters attack rate of SARS-CoV-2 in the Brazilian Amazon during a largely unmitigated epidemic. Buss, L. F., C. A. Prete, Jr., C. M. M. Abrahim, A. C. Dye, V. H. Nascimento, N. R. Faria and E. C. Sabino et al. (2021). Science 371(6526): 288-292.

[2] Resurgence of COVID-19 in Manaus, Brazil, despite high seroprevalence. Sabino EC, Buss LF, Carvalho MPS, Prete Jr CCA, Crispim MAE, Fraiji NA, Pereira RHM, Paraga KV, Peixoto PS, Kraemer MUG, Oikawa MJ, Salomon T, Cucunuba ZM, Castro MC, Santos AAAS, Nascimento VH, Pereira HS, Ferguson NM, Pybus OG, Kucharski A, Busch MP, Dye C, Faria NR Lancet. 2021 Feb 6;397(10273):452-455.

[3] Genomics and epidemiology of the P.1 SARS-CoV-2 lineage in Manaus, Brazil. Faria NR, Mellan TA, Whittaker C, Claro IM, Fraiji NA, Carvalho MDPSS, Pybus OG, Flaxman S, Bhatt S, Sabino EC et al. Science. 2021 Apr 14:eabh2644.

[4] GRINCH Global Report Investigating novel coronavirus haplotypes. PANGO Lineages.

[5] COVID Data Tracker. Variant Proportions. Centers for Disease Control and Prevention.

[6] Antibody evasion by the P.1 strain of SARS-CoV-2. Dejnirattisai W, Zhou D, Supasa P, Liu C, Mongkolsapaya J, Ren J, Stuart DI, Screaton GR, et al. Cell. 2021 Mar 30:S0092-8674(21)00428-1.

Links:

COVID-19 Research (NIH)

Brazil-UK Centre for Arbovirus Discovery, Diagnosis, Genomics and Epidemiology (CADDE)

Nuno Faria (Imperial College, London, U.K.)

Samir Bhatt (Imperial College)

Ester Cerdeira Sabino (Universidade de Sao Paulo, Brazil)

NIH Support: National Institute of Allergy and Infectious Diseases


Israeli Study Offers First Real-World Glimpse of COVID-19 Vaccines in Action

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COVID-19 Update: Large scale clinical trial
Credit: Getty Images/Hispanolistic

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 [1] 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 [2].

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.

References:

[1] 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.

[2] Emerging SARS-CoV-2 Variants. Centers for Disease Control and Prevention.

Links:

COVID-19 Research (NIH)

Clalit Research Institute (Tel Aviv, Israel)

Ran Balicer (Clalit Research Institute)