(CNN) – Since the beginning of the pandemic, scientists have been seeking to better understand immunity to the new coronavirus. How long is a person immune after having COVID-19, after getting vaccinated, or both? And what could lasting immunity mean for vaccine boosters?
It’s still too early to tell, but experts are getting closer to cracking the code.
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What are vaccine boosters?
What is currently known about boosters in the coronavirus vaccine suggests they may be needed at some point, but when, exactly, is not yet clear, Dr. Peter Marks, director of the Center for Biological Research and Evaluation, said Thursday. from the U.S. Food and Drug Administration during a Vaccine Equity and Education Project Webinar.
“We will have to see where all this interacts. Is it possible that we will need a booster at some point? Yes. Is it likely? Yes. Do we know exactly when? No, ”said Marks. “But if I were to look at my crystal ball, it would probably not be earlier, hopefully a year after being vaccinated, for the average adult.”
And, experts emphasize, anyone who is currently fully vaccinated should be protected. But the reason the timeline for boosters remains unclear is because scientists still need time to collect the data on how long immunity against COVID-19 may last in the future, and how to account for those. future variants.
Will a third dose or booster dose of the covid-19 vaccine be necessary?
When a person has “immunity,” in general, that means that they have protection against disease. Active immunity can be acquired through vaccination or infection. Your immune system develops antibodies induced by vaccination or in response to infection, and either immune response can maintain a “memory.”
Immunity is often measured by the presence of antibodies, proteins made by the immune system to help fight infection, in the blood. They can usually be determined with a laboratory test. But immune systems are much more than antibodies; they involve a large number of players, including B cells, which produce antibodies, and T cells, which target infected cells.
Research has shown that both antibodies and T cells could even recognize infections from variants of a pathogen, such as emerging variants of coronaviruses circulating in the world today, which, despite key differences that may cause them to spread. more easily, they have enough similarities to be recognized by the memory of the immune system.
And even if someone has recovered from a previous infection and has natural immunity, vaccines can help boost their immune memory.
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Vaccine manufacturers are monitoring immunity
Currently, three coronavirus vaccines are licensed for emergency use in the United States: the two-dose Pfizer / BioNTech vaccine for ages 12 and older; the Modern two-dose vaccine for those over 18 years of age; and Johnson & Johnson single-dose vaccine for ages 18 and older.
All three companies are investigating the possible use of enhancers.
Vaccine manufacturers have been studying whether the immunity these vaccines elicit can wane over long periods of time, say, possibly after a year or more, and whether they also protect against variants of the coronavirus that could emerge and evolve.
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If so, a vaccinated person might need a booster dose of the vaccine to stay protected against the original coronavirus strain and emerging variants, somewhat similar to how a tetanus booster is recommended every 10 years, or different vaccines are recommended. against the flu every year.
When it comes to other viruses, a measles attack usually leaves a person immune for life. The same happened with smallpox, before the virus was eradicated in the 1970s through a worldwide vaccination campaign. Proper vaccination against measles and smallpox fully protects against infection.
Immunity is different for respiratory viruses and that’s where vaccine boosters come in
But respiratory viruses like influenza and coronavirus are more complicated. People can get the flu over and over again, and flu vaccines generally provide only partial protection against serious infections and illnesses, as there are usually multiple influenza viruses circulating due to mutations. However, the coronavirus has a slower mutation rate than influenza.
Still, doctors worry that the coronavirus could end up being like the flu, requiring a new vaccine every year because circulating strains mutate rapidly and because the vaccine’s immunity wears off quickly.
In the case of coronavirus vaccines, several studies have evaluated the immune responses elicited by the Moderna and Pfizer vaccines to the original strain of the virus, compared to variants. And “these studies found modest or no defects in cellular immune recognition of the variants,” according to a web page on the US Centers for Disease Control and Prevention website, updated Thursday.
“Thus, cellular immunity can help limit the severity of disease in infections caused by variants that partially escape neutralizing antibodies,” according to the CDC.
It is difficult to predict how the reduced neutralizing activity may affect the effectiveness of the COVID-19 vaccine, but in all studies, the antibody neutralizing activity observed among fully vaccinated people has generally been higher than that observed among people who received it. have recovered from covid-19.
Data from clinical trials suggest that the protection offered by Pfizer and Moderna’s coronavirus vaccines is likely to last at least nine months, Marks of the FDA said in April. But experts have gone to great lengths to point out that that doesn’t mean immunity stops at nine months. It means that this is the maximum time that the trial volunteers have been followed to see what their immunity is and to collect data.
Immunity could last much longer; researchers only need time to evaluate it.
The medical community still needs data to determine the extent to which immunity may decline over time, Dr. Amesh Adalja, a senior researcher at the Johns Hopkins Center for Health Security who was not involved in the study, told CNN in an email on Thursday. the studies.
That degree could be measured according to how people who are fully vaccinated eventually suffer progressive infections at a higher rate, or have infections that are severe enough to require hospitalization.
“For me, that’s the threshold,” said Adalja.
The truth is that studies of natural immunity from a previous infection with the coronavirus have been done for only a little longer than vaccine trials.
The latest findings on long-lasting immunity
Two new studies this week add to the growing body of evidence suggesting that natural immunity to coronavirus after someone recovers from COVID-19 can be long-lasting, possibly at least a year. But that doesn’t mean they shouldn’t get vaccinated. Nor does it mean that immunity lasts forever.
A study, published in the journal Nature on Monday, found that immune cells in the bone marrow of people infected with coronavirus have a “memory” of the infection that can last for a long time.
The other research, published in the journal EClinicalMedicine on Monday, found that covid-19 antibodies were still detectable about 10 months after infection among people who had recovered.
Bone marrow cells can maintain the memory of COVID-19 for at least 11 months after someone is infected. These cells are an “essential” source of protective antibodies, according to the new study published in Nature.
Researchers at Washington University in St. Louis examined blood samples from 77 people previously infected with SARS-CoV-2, the virus that causes Covid-19. The researchers found an initial decrease in the presence of covid-19 antibodies after infection, but between four and 11 months the decrease was less.
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The researchers also examined bone marrow samples taken from 19 previously infected patients, approximately seven and 11 months after infection. The researchers found covid-19 antibodies in 15 of the 19 patients and, unlike the decrease in other antibodies observed, those produced by bone marrow cells appeared to remain stable.
“It is good news that these antibodies are being generated and maintained,” Ali Ellebedy, study author and associate professor at Washington University in St. Louis, told CNN’s John Berman on Thursday.
But he added that the findings do not suggest that people who have had COVID-19 no longer need to be vaccinated. Rather, vaccination could further enhance the natural immune response.
“I think people who have become infected and produce this beautiful memory over time would be a great incentive to get the vaccine because now they can put these memory cells into action,” Ellebedy said, adding that having antibodies does not mean that a person is fully protected.
“Our data explains why those who experienced a mild SARS-CoV-2 infection in the past year are generating such amazing responses to vaccination. It’s because of the robust immune memory they developed after infection, “Ellebedy told CNN in an email Thursday.
Some people don’t make enough antibodies
“However, not all previously infected people are the same,” he added. “For many different reasons, some people do not have a strong immune response to infection even after surviving the infection. Therefore, it is better that they receive both vaccines ”, for those who get a two-dose vaccine.
For the same reasons, whether due to age or immunosuppression, some people may be advised to follow a different booster schedule than others in the future if booster shots are eventually needed.
Up to 9 out of 10 people infected with the coronavirus develop natural immunity against the virus that is “maintained with little decomposition” for up to 10 months after the initial infection, suggests the EClinicalMedicine study, conducted by researchers from the national clinical laboratory Labcorp.
The researchers found that about 90% of recovered COVID-19 patients evaluated in the study had detectable antibodies 21 days after infection, and antibody rates remained around 90%, with some variability, up to 300 days.
The researchers analyzed data from 39,086 people who were confirmed to have COVID-19 between March 2020 and January 2021, and had at least one antibody test with Labcorp after testing positive for the coronavirus infection.
The data did not include patient demographic information or information on the severity of a particular covid-19 case.
“More research needs to be done to understand what type and level of antibodies suggest protection against reinfection,” Dr. Brian Caveney, medical director and president of Labcorp Diagnostics, said in a news release Monday. “But the prolonged presence of certain antibodies is a promising sign as we continue to think about safely exiting the pandemic, as well as future vaccines and at the time of booster shots.”
CNN’s Maggie Fox, Ryan Prior, and Naomi Thomas contributed to this report.
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