Recent scientific studies have raised concerns and generated headlines after they suggested that antibodies to the coronavirus fade within months. But scientists say the story is more complicated — and less depressing than it seems.
Here, compiled from Globe wire services and major media reports, is a brief rundown of what people are talking about:
- People infected with the coronavirus, SARS-CoV-2, typically produce immune molecules called antibodies to battle the virus. Several research teams have recently reported that the levels of these antibodies decline in two to three months. One study, described this week in a letter in the New England Journal of Medicine by researchers from the University of California Los Angeles, found that the antibodies had a half-life of 36 days, which means that half of them would be gone after that much time. The researchers said the results “call for caution regarding antibody-based ‘immunity passports,' herd immunity, and perhaps vaccine durability.”
- What’s the big deal? The idea of fading antibodies to the virus raised the specter that people could get sick again even if they have already had the coronavirus; that we could fail to reach herd immunity, where most of the population has become immune; and that vaccines, which provoke the immune system to make antibodies, might provide only temporary protection.
- Scientists, however, are saying there’s more to the story. A drop in antibodies is perfectly normal after an acute infection subsides, said Dr. Michael Mina, an immunologist at the Harvard T.H. Chan School of Public Health. Many clinicians are “scratching their heads saying, ‘What an extraordinarily odd virus that it’s not leading to robust immunity,’ but they’re totally wrong,‘” Mina told The New York Times. “It doesn’t get more textbook than this.”
Scott Hensley, a virologist at the University of Pennsylvania, tweeted that a contraction of the immune system after viral infection is “basic immunology.”
Shane Crotty, a virologist at the La Jolla Institute for Immunology, told The Atlantic, “It’s not unusual to have fading antibody response after several months.”
“The drop-off isn’t that surprising. When you look at something like the smallpox vaccine, you see the antibody response is down about 75 percent after six months. But that’s a vaccine that works for decades,” Crotty said.
- Other research suggests the antibody levels decline and then stabilize. In a study of nearly 20,000 people posted to the online server MedRxiv last week, the vast majority made plentiful 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 god the antibodies are going down’ headlines, but a lot of data suggests a slow and expected decline over months - which I think is normal,” Krammer said Tuesday in a tweet.
- Scientists also emphasize that the antibodies aren’t the only defense the body has against the coronavirus. Memory B cells are a type of white blood cell that creates antibodies based on past skirmishes with pathogens. T cells, another type of white blood cell, also play crucial roles — orchestrating the entire immune response, instructing the body to create more antibodies and even actively fighting the virus by killing infected cells, The Washington Post reported.
“Even if you don’t have a very high level of antibodies, you may be able to respond very rapidly to a challenge and nip it in the bud — and that’s because you have memory cells that remember,” Michel Nussenzweig, head of the laboratory for molecular immunology at Rockefeller University, told the Post. “You may be able to produce a better response the second time around, a faster response the second time around. So even if you’re exposed to the virus, you may have an aborted infection or something that is very mild.”
“Antibodies wane after a certain period of time,” Thomas Schinecker, who heads the diagnostics unit of Swiss drugmaker Roche Holding AG, told Bloomberg News. “This doesn’t mean that there is no immunity, it just means that potentially the memory cells, T cells and others, will then be triggered to respond much better the second time so that you don’t have any severe response.”
- Whatever the body’s mechanism for fighting the virus is, it may be working for now. Despite a growing number of anecdotal accounts of people getting sick twice from the coronavirus, there is no scientific proof that it can happen. “I haven’t heard of a case where it’s been truly unambiguously demonstrated,” Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health, told the Times.
“No one is yet believing in reinfection since 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, no one wants to dismiss the possibility.”
- While the scientists say the recent antibody studies aren’t the end of the world, it’s still a mystery exactly how long immunity will last after someone gets infected or receives a vaccine.
Immunity to some diseases can last for a person’s lifetime. But the familiar coronaviruses that cause the common cold can infect people over and over.
Krammer, the scientist from the Mount Sinai School of Medicine, cautiously ventured an estimate, telling NPR: “It’s reasonable to assume that there will be protection for a time frame of one to three years. But of course, we are scientists. We have to prove that, right? That’s why everyone’s cautious about it. But I think that’s a pretty fair assumption.”
Material from Globe wire services was used in this report.
Martin finucane can be reached at firstname.lastname@example.org