Antibodies From Mild Covid Symptoms May Not Give Lasting Protection, Bodes Badly For Vaccines, Immunity
People who have had covid-19 might not be immune from catching it again. New studies show that antibodies against the virus don’t last. This doesn’t bode well for potential vaccines or for immunity.
“Antibodies are proteins that white blood cells called B cells make to bind to the virus and help eliminate it. The earliest ones are fairly crude but as infection goes on, the immune system becomes trained to focus its attack and to make more precise antibodies,” NBC News reported.
Correspondence in the New England Journal of Medicine recently outlined research on antibodies taken from the blood of 34 patients who had recovered after suffering mainly mild symptoms that didn’t require intensive care, Bloomberg reported.
In the first testing, antibodies were taken an average of 37 days after symptoms began, with a second after about 86 days, or less than three months. Unlike previously thought, the antibodies were not long-lasting. Here, researchers found that antibody levels dropped quickly, with a half-life of about 73 days between the two time frames.
These findings were concerning because they mean that protection from reinfection may not last long in those with mild symptoms, Bloomberg reported.
Another study from King’s College London recently showed that the level of antibodies may drop to a degree that makes them undetectable as soon as three months after infection. “However, the body also mounts other forms of immunity responses, including from so-called T-cells, which appear to play a role in protecting against reinfection with covid-19,” Bloomberg reported.
According to Sweden’s top health authority, six months might be the period of immunity for people who previously had the virus, even though the New England Journal of Medicine research suggests that antibodies last just about three months.
“In short, though antibodies have proved invaluable for tracking the spread of the pandemic, they might not have the leading role in immunity that we once thought. If we are going to acquire long-term protection, it looks increasingly like it might have to come from somewhere else,” The BBC reported.
“Infection with this coronavirus does not necessarily generate lifetime immunity,” but antibodies are only part of the story,” Dr. Buddy Creech, an infectious disease specialist at Vanderbilt University,” told NBC News. He had no role in the New England Journal of Medicine research.
Although circulating antibodies may not last long, what vaccine researchers need to discover is if and how people remake antibodies if exposed to the coronavirus again and if they protect against another infection, Alison Criss, an immunologist at the University of Virginia, wrote in an email to NBC News. “We also need to know if there is a protective T cell response” that reappears.
Vaccines would provoke the immune system to make antibodies. And, vaccines might give longer-lasting protection than natural infection because they use purified versions of what stimulates that response, she noted.
Antibodies, however, might not be the solution as researchers have begun to realize that there might be another form of immunity – an enigmatic type of white blood cell is gaining attention.
Researchers tested blood samples taken years before the pandemic started, and they found T cells could detect proteins on the surface of covid-19.
“T cells are a kind of immune cell, whose main purpose is to identify and kill invading pathogens or infected cells. It does this using proteins on its surface, which can bind to proteins on the surface of these imposters. Each T cell is highly specific – there are trillions of possible versions of these surface proteins, which can each recognize a different target. Because T cells can hang around in the blood for years after infection, they also contribute to the immune system’s ‘long-term memory’ and allow it to mount a faster and more effective response when it’s exposed to an old foe,” The BBC reported.
In several studies, it was found that people infected with covid-19 usually have T cells that can target the virus. This suggests that some people already had a pre-existing degree of resistance against the virus before it ever infected a human.
“But scientists have also recently discovered that some people can test negative for antibodies against covid-19 and positive for T cells that can identify the virus. This has led to suspicions that some level of immunity against the disease might be twice as common as was previously thought,” The BBC reported.
“Looking at covid-19 patients – but also I’m happy to say, looking at individuals who have been infected but did not need hospitalization – it’s absolutely clear that there are T cell responses,” concluded Adrian Hayday, an immunology professor at King’s College London and group leader at the Francis Crick Institute. “And almost certainly this is very good news for those who are interested in vaccines, because clearly we’re capable of making antibodies and making T cells that see the virus. That’s all good.”
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Covid researchers can’t celebrate just yet. In many patients who are hospitalized with more serious covid-19, the T cell response hasn’t quite gone to plan.
“Vast numbers of T cells are being affected,” says Hayday. “And what is happening to them is a bit like a wedding party or a stag night gone wrong – I mean massive amounts of activity and proliferation, but the cells are also just disappearing from the blood.”