Antibodies to the coronavirus may provide protection against re-infections even if they wane over time, according to experts, who say people shouldn’t be alarmed by recent studies that have had seemingly conflicting results.
Antibodies and other immune responses have been at the center of coronavirus research, as there are important implications for how long people are protected before a vaccine is available. If the antibodies provide long-lasting immunity, for example, people who have been infected can be protected until there is a viable vaccine. But the decrease in antibodies could mean that Covid-19 survivors may be at risk of reinfection.
Two studies published this week have raised some confusion because of their divergent results. An article published in the journal Science, led by scientists from New York, found that Covid-19 antibodies developed by the immune system persisted at stable levels for about five months. But two days earlier, a pre-printed study that has yet to be peer reviewed found that among hundreds of thousands of participants across England, antibody levels have declined rapidly, dropping over 26% over a three-month period.
Most experts agree that drops in antibody levels over time are expected and that these drops are not of concern at all.
“If you think about basic immunology, you should have an antibody response to start with, then that antibody response should go away,” said Ritesh Tandon, associate professor of microbiology and immunology at the University of Mississippi Medical Center. , who did not participate in either. study. “Antibodies are dynamic – they are not made once and stay in the blood.”
Dr Anthony Fauci, the nation’s leading infectious disease specialist, echoed the sentiment, adding that lower antibody levels don’t necessarily translate into lack of immunity.
“Just because the antibody level is dropping doesn’t mean you lose protection,” he said in a National Institutes of Health briefing Thursday.
In the recent study published in Science, researchers at the Icahn School of Medicine at Mount Sinai used a database of the immune responses of 30,000 New Yorkers who tested positive for the coronavirus between March and October and monitored 121 volunteers over time.
The researchers found that antibody responses peaked about two to three months after infection. And in 90% of people who recovered, antibody levels subsequently dropped but remained stable for about five months, said Dr Ania Wajnberg, associate professor of medicine at Icahn School of Medicine and co. -author of the Mount Sinai study.
“The majority of patients have a relatively robust response and so far it persists over time,” she said.
In the UK study, scientists at Imperial College London found that the prevalence of antibodies in UK participants had increased from 6% at the end of June to 4.4% in September. And using home tests that were distributed to more than 365,000 people, the researchers observed a more than 26% drop in antibody levels over three months.
But there were limits with the British study. Although the study had hundreds of thousands of participants, the researchers did not follow the same people over time. The study also did not accurately measure antibody levels.
“The sensitivity between the two tests is a major difference,” said Alan Wu, professor of laboratory medicine at the University of California, San Francisco, who was not involved in either study. “It’s a bit like apples and oranges, in the sense that studies are not done the same way.”
But despite the apparently divergent results of the two studies, they may both be true, according to Dr. Arturo Casadevall, director of the Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health. It is not unreasonable – nor particularly alarming – if antibody levels decline quickly after a person heals, then persist for a while at a much lower level, he said.
“We know that other coronaviruses tend to elicit immunity that doesn’t last long,” Casadevall said. “The question is: how many antibodies do you need to avoid reinfection? You may need very little.
However, antibodies are not the only weapons in the arsenal of the immune system. There are cellular immune responses that could recognize a virus and provide some protective immunity. People who have been infected with a virus also usually produce “memory cells” that can recall certain pathogens and quickly mobilize a defense against reinfection.
“Antibody immunity is only part of immunity,” Casadevall said. “If you have an immunological memory, it means that if you face the coronavirus again, your body doesn’t need two weeks to figure out how to react. This memory could come into play right away.
There’s no easy way to detect memory cells and cellular immune responses in recovered patients, but it’s an active area of research, according to Tandon. And so far, immune responses to the coronavirus are more or less in line with those of other known coronaviruses, he added.
“It follows the rules of immunology – it’s not some foreign virus that we seem to know nothing about,” Tandon said. “I haven’t seen anything that makes me think this is a very different virus than anything we’ve seen before.”