– What is the problem? The idea of fading out the antibodies against the virus raised the specter that people could get sick again even if they had already had the coronavirus; that we could not achieve immunity from the herd, where the majority of the population has become immune; and that vaccines, which cause the immune system to produce antibodies, can only provide temporary protection.
– However, scientists say there is more to the story. A drop in antibodies is perfectly normal after an acute infection subsides, said Dr. Michael Mina, an immunologist at Harvard’s TH Chan School of Public Health. Many doctors are “scratching their heads saying, ‘What a strange virus that is not leading to robust immunity,’ but they are totally wrong,” Mina told the New York Times. “There are no more textbooks than this.”
Scott Hensley, a virologist at the University of Pennsylvania, tweeted that a contraction of the immune system after a viral infection is “basic immunology.”
Shane Crotty, a virologist at the La Jolla Institute of Immunology, told The Atlantic: “It is not unusual to have an antibody response that fades after several months.”
“The return is not that surprising. When you look at something like the smallpox vaccine, you see that the antibody response has dropped about 75 percent after six months. But that’s a vaccine that works for decades ” Crotty said.
– Other research suggests that antibody levels drop and then stabilize. In a study of nearly 20,000 people published on MedRxiv online server last week, the vast majority made abundant antibodies, and half of those with low levels still had antibodies that could destroy the virus.
“None of this is really surprising from a biological point of view,” Florian Krammer, an immunologist at the Icahn Mount Sinai School of Medicine who led that study, told The Times.
“There are a lot of ‘oh my gosh, the antibodies are going down’ headlines, but a lot of data suggests a slow and expected decline for months, which I think is normal,” Krammer said Tuesday in a tweet.
– Scientists also emphasize that antibodies are not the only defense the body has against the coronavirus. Memory B cells are a type of white blood cell that create antibodies based on past skirmishes with pathogens. T cells, another type of white blood cell, also play crucial roles: they orchestrate the entire immune response, instruct the body to create more antibodies, and even actively fight the virus by killing infected cells, The Washington Post reported.
“Even if you don’t have a very high antibody level, you may be able to respond very quickly to a challenge and nip it in the bud, and that’s because you have memory cells that remember,” Michel Nussenzweig, head of the molecular immunology laboratory at the Rockefeller University told the Post. “You may be able to produce a better response the second time, a faster response the second time. So even if you’re exposed to the virus, you might have an aborted infection or something very mild. “
“The antibodies decrease after a certain period of time,” Thomas Schinecker, who heads the diagnostic unit at Swiss pharmaceutical firm Roche Holding AG, told Bloomberg News. “This does not mean that there is no immunity, it just means that memory cells, T cells and others, will potentially activate to respond much better the second time so you don’t have a severe response.”
Whatever the body’s mechanism is to fight the virus, it may be working for now. Despite the growing number of anecdotal accounts of people getting sick twice from the coronavirus, there is no scientific evidence that it can happen. “I have not heard of a case in which it has been unequivocally demonstrated,” Marc Lipsitch, an epidemiologist at the Harvard TH Chan School of Public Health, told the Times.
“No one believes in reinfection yet as there is no good scientific report on it,” Monica Gandhi, a professor of medicine and associate chief of infectious diseases at the University of California, San Francisco, told the Post. “On the other hand, nobody wants to rule out the possibility.”
– While scientists say recent antibody studies are not the end of the world, it remains a mystery exactly how long immunity will last after someone becomes infected or receives a vaccine.
Immunity to some diseases can last a person’s entire life. But the well-known coronaviruses that cause the common cold can infect people over and over again.
Krammer, the scientist at Mount Sinai School of Medicine, cautiously ventured an estimate and told NPR: “It is reasonable to assume that there will be protection for a period of one to three years. But of course we are scientists. We have to demonstrate that, right? That is why everyone is cautious about it. But I think that’s a pretty fair guess. “
Wire Globe services material was used in this report.
Martin Finucane can be contacted at [email protected]
