Be careful not to jump to conclusions.
ANDOn this day, a preprint that was recently released on the medRxiv server (meaning the study hasn’t undergone peer review, an important step for accurate scientific research) generated a surge of excitement, and criticism, for its implication that immunity to the coronavirus could last only a few months. The document suggested that the levels of antibodies that people produce in response to Covid-19 infection drop rapidly after reaching their peak.
The newspaper’s findings, which were covered by large media such as The GuardianCNBC and CNN suggest that people’s immunity after a Covid-19 infection declines over time. And that does not seem to bode well for hopes of collective immunity or a vaccine. A couple of days before Vox He published a story written by a doctor suggesting that a patient who recovered from Covid-19 was reinfected, raising similar concerns about immunity to the coronavirus.
But as critics pointed out on Twitter, these case studies should be part of a broader understanding and study of Covid-19 and immunity. The study has not yet been reviewed by scientists, and the Vox History is a unique opinion piece on a case. Importantly, this framework also assumes that antibodies are the only way to achieve immunity, which is simply not the case.
In the medRxiv study, researchers at King’s College London repeatedly tested the antibody levels of 96 people who tested positive for Covid-19 between March and June. They found that while 60% of people had a “potent” antibody response around 23 days after their symptoms appeared, only 16.7% of them still had the same level of potency on average 65 days. after. They also found that people who had more severe Covid-19 infections tended to have more longer-lasting antibodies than people with milder cases.
Taken together, the findings raised concerns that the antibodies cannot be relied upon to provide lasting protection to the virus, which is concerning, given that a successful vaccine is generally regarded as one that produces long-lasting antibodies.
But antibodies are not the only way the body can fight Covid-19, thanks to the existence of multiple branches of the immune system. It’s understandable if you didn’t know they exist: Over the course of the pandemic, many scientific experts and communicators (including myself) have written about immunity only where antibodies are concerned, but the reality is far more complex than that.
The antibody-mediated branch of the immune system has been widely discussed during the pandemic, specifically, its ability to respond to infection by producing neutralizing antibodies, the type that can fight the virus in future encounters. Neutralizing antibodies are those that prepress refers to, that vaccines are intended to produce, that antibody tests attempt to detect, and that are sought in convalescent plasma. But there are many more types of antibodies that also work for immunity; they just haven’t been talked about as much.
The other major branch of the immune system is known as cellular immunity or cellular immunity. It doesn’t have much to do with antibodies at all. Instead, it relies on two types of immune cells, B cells and T cells, which have different methods of fighting the pathogens they have previously found. There is an ongoing investigation into cellular immunity to Covid-19, but not much has been said about it, either. If antibody-mediated immunity plays a limited role in Covid-19 infection, cellular immunity may be a much-needed alternative or complement.
I keep going back to a Twitter thread from Eric Topol, MD, president of Innovative Medicine at Scripps Research, on how to think about new research on immunity and the coronavirus. In it, he emphasizes the importance of recognizing the other branches of the immune system. “So when you interpret the seroprevalence, serology, antibody-only data, keep the incomplete nature of that assessment in terms of the broader cellular immune response to # SARSCoV2,” he writes. “There is much more to learn about things that we don’t measure.” It also points to research showing that cells that are not normally considered part of the immune system, such as those of the thymus or liver, have their own immune response to the coronavirus.
Several questions remain unanswered about reports of people testing positive for Covid-19 after they apparently recovered from the virus. Are they having a relapse of symptoms, or did they really catch Covid-19 a second time? Scientists are still working on the possibilities.
A newsletter from the Johns Hopkins Center for Health Safety sent out today similarly warns readers about the interpretation of the medRxiv document and the Vox history. The “duration of immunity is unclear,” he says, and “it is not known whether or not recurrent infections are related to diminishing immunity after initial infection.” Furthermore, she points out that just because a person tests positive for antibodies does not mean that they are protected against reinfection, since antibody tests do not necessarily detect the neutralizing antibodies necessary for immunity.
In a blog post released today, Francis Collins, MD, director of the National Institutes of Health, acknowledges “rare reports” of people recovering from Covid-19 only to test positive again. (Although he does not specify which reports.) He says that “these results could be explained by reports that the virus can remain in our systems,” but reiterates that many questions remain about immunity. Collins notes that in a recent study, macaques that had been deliberately infected with Covid-19 mounted a protective antibody response when they were reinfected 28 days later.
None of this is to say that the King’s College London study or the case study described in Vox It cannot be significant, only that their findings (which must be studied and replicated before strong evidence is considered) represent only part of the potential immune response to Covid-19. It is useful to keep this in mind when thinking about the recent recognition by the World Health Organization that antibodies can decrease after several months and the recent study by the Spanish government that found that antibodies could disappear after a few weeks . It is not known if the antibodies last a long time, if they really protect us from reinfection and if cellular immunity has a role to play, but at the moment, not being sure how to answer these questions leaves us in a better state than answering them definitively. with a “no”.
