- It might last for years, even decades, which is the most hopeful answer yet to a question that has shadowed plans for widespread vaccination.
- Eight months after infection, most people who have recovered still have enough immune cells to fend off the virus and prevent illness.
- A slow rate of decline in the short term suggests that these cells may persist in the body for a very, very long time to come.
Blood samples from recovered patients suggest a powerful, long-lasting immune response, according to The New York Times.
MORE ABOUT THE RESEARCH
It has not been peer-reviewed nor published in a scientific journal. But It is the most comprehensive and long-ranging study of immune memory to the coronavirus to date. The findings are likely to come as a relief to experts worried that immunity to the virus might be short-lived, and that vaccines might have to be administered repeatedly to keep the pandemic under control, according to Shane Crotty, a virologist at the La Jolla Institute of Immunology says, “that amount of memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years.”
SOME OTHER RELATED STUDIES
Researchers at the University of Washington, led by the immunologist Marion Pepper, had earlier shown that certain “memory” cells that were produced following infection with the coronavirus persist for at least three months in the body. A study published last week also found that people who have recovered from Covid-19 have powerful and protective killer immune cells even when antibodies are not detectable.
WHAT ARE THE DOCTORS SAYING?
Akiko Iwasaki, an immunologist at Yale University, said she was not surprised that the body mounts a long-lasting response because “that’s what is supposed to happen.”
These studies “are all by and large painting the same picture, which is that once you get past those first few critical weeks, the rest of the response looks pretty conventional,” said Deepta Bhattacharya, an immunologist at the University of Arizona.
Although a small number of infected people in the new study did not have long-lasting immunity after recovery, vaccines can overcome that individual variability, said Jennifer Gommerman, an immunologist at the University of Toronto. “That will help in focusing the response, so you don’t get the same kind of heterogeneity that you would see in an infected population,” she said.
ANTIBODIES AND HOW THEY ARE WORKING
Although antibodies in the blood are needed to block the virus and forestall a second infection — a condition known as sterilizing immunity — immune cells that “remember” the virus more often are responsible for preventing serious illness. Although reports of waning antibody levels have created worry that immunity to the coronavirus may disappear in a few months, leaving people vulnerable to the virus again, many immunologists have noted that it is natural for antibody levels to drop. Besides, antibodies are just one arm of the immune system.
Exactly how long immunity lasts is hard to predict, because scientists don’t yet know what levels of various immune cells are needed to protect from the virus. But studies so far have suggested that even small numbers of antibodies or T and B cells may be enough to shield those who have recovered.
HOW THE BODY DEALS WITH A SECOND INFECTION
If people become infected a second time with a particular pathogen, and the immune system recognizes the invader and quickly extinguishes the infection. The coronavirus in particular is slow to do harm, giving the immune system plenty of time to kick into gear. It may be terminated fast enough so that there will neither be any symptoms, nor will it be infectious.
There is some emerging evidence that reinfections with common cold coronaviruses are a result of viral genetic variations and so those concerns may not be relevant to the new coronavirus.
THE TEAMS AND THEIR RESEARCH
Dr. Sette and his colleagues recruited 185 men and women, aged 19 to 81, who had recovered from Covid-19. The majority had mild symptoms not requiring hospitalization; most provided just one blood sample, but 38 provided multiple samples over many months.
The team tracked four components of the immune system: antibodies, B cells that make more antibodies as needed; and two types of T cells that kill other infected cells. The idea was to build a picture of the immune response over time by looking at its constituents.
Researchers found that antibodies were durable, with modest declines at six to eight months after infection, although there was a 200-fold difference in the levels among the participants. T cells showed only a slight, slow decay in the body, while B cells grew in number — an unexpected finding the researchers can’t quite explain. The study is the first to chart the immune response to a virus in such granular detail, experts said.
One frequently cited study, led by Jeffrey Shaman of Columbia University, suggested that immunity might fade quickly and that reinfections could occur within a year. “What we need to be very mindful of is whether or not reinfection is going to be a concern,” Dr. Shaman said. “And so seeing evidence that we have this kind of persistent, robust response, at least to these time scales, is very encouraging.”
“There’s no sign that memory cells are suddenly going to plummet, which would be kind of unusual,” Dr. Iwasaki said. “Usually, there’s a slow decay over years.”
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Source: The New York Times
