iStockThrust into focus by recent studies, T cells are a reminder that the body's defenses rely on more than one weapon, and that much of the immune response to Covid-19 is still a mystery - especially after researchers revealed that the more lauded antibodies lack staying power.
A study published July 15, for example, looked at three different groups. While these T cells may not be strong enough to prevent someone from contracting COVID-19, they could explain why so many cases are asymptomatic or only generate mild symptoms. When a new virus is first encountered, more generalized forms of antibodies are quickly produced, but their specificity against the virus gets increasingly precise as time goes on.
Based on blood tests collected up to 119 days after the onset of symptoms, the researchers said the half-life of antibodies linked with SARS-CoV-2 infection was just 36 days - just over a month.
At that rate, antibodies would disappear within a year.
So-called helper T cells, as well as memory T and B cells are able to prime antibodies to respond to a subsequent infection before it causes severe symptoms, said Smith, who is studying the immune response to the SARS-CoV-2 virus.
The team says the findings 'call for caution regarding antibody-based "immunity passports", herd immunity, and perhaps vaccine durability'.
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"Now there are two studies, one from Spain and one from the United Kingdom, that actually measures the virus in people and the antibodies and watching the immunity decline", said Haseltine.
But that doesn't mean that immunity necessarily is gone, he added, since the human immune system has other tricks up its sleeve.
"They would get called vigorously immediately when there's another presentation to the infection. It's as if they lie dormant, just waiting", he said.
'Although circulating antibodies may not last long, what we need to know is if and how people remake antibodies if exposed to the coronavirus again and if they protect against another infection, ' Dr Alison Criss, an immunologist at the University of Virginia, wrote in an email.
The study period was 90 days, so additional studies are needed to see the long-term effects, they added, but it's likely that antibodies continue to decline after that.
"This shouldn't dissuade us from pursuing a vaccine", Creech said. The resistant framework recalls how to make new antibodies if necessary to mount an assault, Creech included.