It’s still too early to tell, but experts are getting closer to cracking the code.
“We’ll have to see where it all interacts. Is it possible that we need a reminder at some point? Yes. Is it likely? Yes. Do we know exactly when? No, ”Marks said. “But if I were to look at my crystal ball, it’s probably not sooner, hopefully, than a year after being vaccinated, for the average adult. “
And, experts point out, anyone who is currently fully vaccinated should always be protected. But the reason the timing of potential boosters remains uncertain is that scientists still need time to collect the data on how long Covid-19 immunity will last in the future – and how to account for future variants.
Immunity is often measured by the presence of antibodies – proteins made by the immune system to help fight infections, in the blood. They can usually be determined by a lab test. But immune systems are more than just antibodies; they involve a multitude of actors including B cells, which produce antibodies, and T cells, which target infected cells.
Research has shown that antibodies and T cells could even recognize infections from variants of a pathogen – such as the emerging variants of the coronavirus circulating around the world today, which despite key differences that may make them more easily, have enough similarities to be recognized by the memory of the immune system.
And even if a person has recovered from a previous infection and has natural immunity, vaccinations can help strengthen their immune memory.
Vaccine makers monitor 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 two-dose Moderna vaccine for those 18 and over; and the Johnson & Johnson single dose vaccine for those 18 and over.
All three companies are studying the potential use of boosters.
Vaccine makers have studied whether the immunity these vaccines elicit can wane over long periods of time – say, maybe after a year or more – and whether they also protect against variants of the coronavirus that might emerge and evolve. .
If this is the case, a vaccinated person may need a vaccine booster dose to stay protected against the original strain of coronavirus and emerging new variants – somewhat similar to how a tetanus booster is recommended all. every 10 years, or different flu shots are recommended each year.
As for other viruses, a single measles attack usually leaves a person immune for life. The same was true for smallpox, before this virus was eradicated in the 1970s by a global vaccination campaign. Proper vaccination against measles and smallpox completely protects against infection.
But respiratory viruses such as influenza and coronavirus are trickier. People can get the flu over and over again, and flu shots usually offer only partial protection against serious infections and illnesses, as several flu viruses usually circulate due to a mutation. However, the coronavirus has a slower mutation rate than the flu.
Still, doctors fear the coronavirus will end up looking like the flu, which requires a new vaccine every year both because circulating strains mutate quickly and because the vaccine’s immunity wears off quickly.
In the case of coronavirus vaccines, several studies have evaluated the immune responses induced by Moderna and Pfizer vaccines to the original strain of the virus, compared to variants. And “these studies have observed modest or no defects in cellular immune recognition of variants,” according to a website on the US Centers for Disease Control and Prevention website, updated Thursday.
“Thus, cellular immunity may 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 reduced neutralizing activity may affect the effectiveness of the Covid-19 vaccine – but in all studies, the neutralizing activity of antibodies seen in fully vaccinated people was generally higher than that seen in people. who have recovered from Covid-19.
Clinical trial data suggests that the protection offered by the Pfizer and Moderna coronavirus vaccines likely lasts at least nine months, FDA Marks said in April. But experts have made a point of stressing that this does not mean that immunity ends at nine months. This means that the longest volunteers in the trials were followed to see their immunity and collect data.
Immunity could last much longer; researchers just need time to assess.
The medical community still needs data to determine how much immunity may wane over time, Dr. Amesh Adalja, a senior researcher at the Johns Hopkins Center for Health Security who was not involved in the studies, told CNN on Thursday. .
This degree could be measured as if people who are fully vaccinated possibly have breakthrough infections at a higher rate, or have infections severe enough to require hospitalization.
“For me, that’s the threshold,” Adalja said.
Meanwhile, studies of natural immunity to previous coronavirus infection have been underway for a bit longer than vaccine trials.
The latest findings on lasting immunity
Two new studies this week add to the growing body of evidence that suggests that natural immunity to the coronavirus after a person has recovered from Covid-19 may be long lasting – perhaps at least a year . But that doesn’t mean they shouldn’t get the vaccine. It also doesn’t mean that immunity will last forever.
A study, published Monday in the journal Nature, found that immune cells in the bone marrow of people infected with the coronavirus have a “memory” of the infection that can last for a long time.
The other research, published Monday in the journal EClinicalMedicine, found that Covid-19 antibodies remained detectable around 10 months after infection in people who had recovered.
Bone marrow cells can retain a memory of Covid-19 for at least 11 months after a person is infected. These cells are an “essential” source of protective antibodies, according to the new study published in Nature.
Researchers at the University of Washington in St. Louis examined blood samples from 77 people previously infected with SARS-CoV-2, the virus that causes Covid-19. Researchers found an initial decrease in the presence of Covid-19 antibodies after infection, but between four and 11 months the decline slowed.
The researchers also looked at bone marrow samples taken from 19 previously infected patients, around seven and 11 months after infection. Researchers found Covid-19 antibodies in 15 of 19 patients – and unlike the decline in other antibodies observed, those produced by bone marrow cells appeared to remain stable.
“It’s 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 results do not suggest that people who have had Covid-19 no longer need to be vaccinated. On the contrary, vaccination could further enhance the natural immune response.
“I think people who have been infected and who produce this beautiful memory over time, that would be a great incentive to get the vaccine because now you can put those memory cells into action,” Ellebedy said, adding that having antibodies does not mean a person is completely protected.
“Our data explains why those who have had a mild SARS-CoV-2 infection in the past year generate such impressive responses to vaccination. It’s because of the robust immune memory they developed after infection, ”Ellebedy told CNN in an email Thursday. .
“However, not all previously infected people are the same,” he added. “For many different reasons, some individuals do not generate a robust immune response to infection even after surviving infection. It is therefore preferable that they receive both vaccinations ”, for those who receive a two-dose vaccine.
For these same reasons – whether due to age or being immunocompromised – some people may be advised to take a different booster schedule than others in the future, if taking injections of reminder may be necessary.
Up to 9 in 10 people infected with the coronavirus develop a natural immunity to the virus that is “sustained with little degradation” for up to 10 months after their initial infection, suggests the EClinicalMedicine study, conducted by researchers in the clinical laboratory national Labcorp.
Researchers found that about 90% of recovered Covid-19 patients tested in the study had detectable antibodies 21 days after infection – and antibody levels remained around 90%, given some variability, up to 300 days.
Researchers analyzed data on 39,086 people who were confirmed to have Covid-19 between March 2020 and January 2021, and underwent at least one antibody test performed with Labcorp after testing positive for coronavirus infection. .
The data did not include patient demographic information or information on the severity of a particular case of Covid-19.
“More research needs to be done to understand what type and level of antibodies suggest protection against reinfection,” Dr. Brian Caveney, chief medical officer and president of Labcorp Diagnostics, said in a press release on Monday. “But the prolonged presence of some antibodies is a promising sign as we continue to think about a safe exit from the pandemic, as well as future vaccinations and the timing of booster shots. “
CNN’s Maggie Fox, Ryan Prior and Naomi Thomas contributed to this report.