How long could Covid-19 immunity last? It’s not just about antibodies

A health worker in Iraq holding a blood sample taken from a recovered covid-19 patient.

A health worker in Iraq holding a blood sample taken from a recovered covid-19 patient.
Photo: Asaad Niazi / AFP (fake pictures)

A recent study doing he rounds Everywhere It is certainly puzzling: He found that previously infected people can lose almost a whole type of antibody to the coronavirus in three months. But the study findings are too limited to assume that immunity to the virus is so short-lived.

The study was published last week in Nature Medicine. Using blood samples, researchers in China studied the immune response of 37 people who tested positive for the coronavirus but never developed any symptoms. They were compared to 37 people who became mildly ill, as well as a control group of people who tested negative for the virus.

Both groups that contracted the virus had relatively similar immune responses at first. But two to three months later, more than 90% of both groups experienced a significant reduction in covid-19 specific IgG antibodies; Most of both groups also experienced a drop in antibodies that prevent the virus from infecting cells, which are called neutralizing antibodies. This decrease in IgG and neutralizing antibodies was more severe for asymptomatic individuals, with around 40% becoming seronegative for IgG, meaning that their levels had dropped beyond the detection point (12% of the symptomatic group also came back negative).

The findings “may indicate the risks of using COVID-19’s ‘immunity passports’,” the scientists wrote. But as you admit, we still need a lot more research to confirm these results and to know if immunity could be so brief.

“Overall, it’s a pretty well-done study,” Otto Yang, professor of medicine and associate chief infectious disease officer at UCLA’s David Geffen School of Medicine, told Gizmodo. “But there are at least two big caveats that have not been much discussed and should be taken into account. ”

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One problem is that antibodies aren’t always the most important thing when it comes to fending off a disease we’ve had before, Yang said.

There are other immune cells that our body creates when a virus or germ we have found before appears again, particularly certain types of T cells. Like antibodies, these cells are specifically encoded to recognize the returning pathogen. And so far, the evidence suggests that being infected with the coronavirus tends to create a strong T-cell response. With some viruses, Otto noted, it is cellular immunity that provides the most protection against reinfection or disease, not antibodies.

“The second caveat is that if the antibodies correlate with immunity, then it is not clear what the limit would be,” Yang said.

We have some evidence of studies from other human coronaviruses whose antibody levels tend to drop significantly after a year or two after infection, and people can be reinfected at that time. Even a year of protection would be more useful than a few months, given continued efforts to create an effective vaccine as soon as possible.

For example, a recent study published in Nature Medicine analyzed blood samples collected from 149 patients recovered an average of 39 days after illness. Although most of these patients appeared to have relatively low levels of neutralizing antibodies, the researchers still found that they provided “potent antiviral activity” in all of the patients evaluated.

Another consideration is memory B cells, which help to speed up the immune system, including the production of antibodies, in response to reinfection. Even if someone’s active antibody levels to the virus behind covid-19 quickly fade, their bodies may continue to mount a powerful and rapid defense against the virus as soon as they try to infect them again. This response may not prevent reinfection, but it should make the second round easier to handle.

“I think it is very reasonable to assume that reinfection would be milder,” said Yang. “Whatever the balance of genetic or underlying factors that determined your disease the first time, it will probably be the same. And, in addition, they will have an initial advantage in terms of the immune responses that were used to clear the infection in the first place, whether antibodies or T cells. ”

As encouraging as it is, the findings definitely have some important implications if they turn out to be valid. If people actually experience drastic drops in antibody levels a few months after infection, using antibody tests as a way to identify people who are supposedly “safe” from the virus will fall flat on their face. It could also mean that we have to examine people early for antibodies if we want to measure how widespread the virus has been in an area and that subsequent detection should not be considered reliable.

It also sheds more on They challenge the notion of using collective immunity (the idea that enough immune people in a population will prevent the virus from spreading to vulnerable yet uninfected segments) to overcome this pandemic, according to Bruce Walker, immunologist and director of the University of Harvard. for AIDS research.

“This suggests that a significant number of people who generate antibodies are going to lose those antibodies. And then they let us speculate. Does that mean that those people are now infectious? Does that mean there might still be some level of immunity that would attenuate a repeated infection and perhaps not even be noticed? Walker said to Gizmodo. “We just don’t know at the moment.”

At the same time, Walker added, this study can only tell us something about natural immunity, not the type of immunity we hope to get from a possible vaccine someday. Some vaccines do provide A more robust and long-lasting immune response than a natural infection.

However, the issue of reinfection and immunity is somewhat debatable at this time, since the vast majority of people in the world and in the US have not yet contracted the virus. This week alone, the Centers for Disease Control and Prevention Dear that 5% to 8% of Americans have had covid-19 so far. Those who are not yet infected include millions of people over the age of 65 or living with chronic diseases such as diabetes that makes them more vulnerable to serious or life-threatening infection. For most of us, it is the first round of the virus that we should be concerned about. But for people who have survived an infection, the findings may emphasize the need to remain safe.

“A take-home message is that if you have already been infected, don’t assume you are no longer infectious,” Walker said. “Wear masks, distancing and disinfection even.”