New findings suggest that almost all Covid-19 survivors have the immune cells necessary to fight re-infection.
The findings, based on analyses of blood samples from 188 Covid-19 patients, revealed that responses to the novel coronavirus from all major players in the “adaptive” immune system, can last for at least eight months after the onset of symptoms from the initial infection.
Lead author, LJI Professor, Alessandro Sette, said in a statement: “Our data suggest that the immune response is there — and it stays.”
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Co-author, Professor Shane Crotty, Ph.D., and LJI Research Assistant Professor Daniela Weiskopf, said: “We measured antibodies, memory B cells, helper T cells and killer T cells all at the same time. As far as we know, this is the largest study ever, for any acute infection, that has measured all four of those components of immune memory.”
The findings, published in the journal Science, stated that Covid-19 survivors have protective immunity against serious disease from the SARS-CoV-2 virus for months, perhaps years after infection.
The new study helps clarify some concerns over Covid-19 data from other labs, which showed a dramatic drop-off of Covid-fighting antibodies in the months following infection. Some feared that this decline in antibodies meant that the body wouldn’t be equipped to defend itself against reinfection.
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Sette explained that a decline in antibodies is very normal. “Of course, the immune response decreases over time to a certain extent, but that’s normal. That’s what immune responses do. They have a first phase of ramping up, and after that fantastic expansion, eventually, the immune response contracts somewhat and gets to a steady state,” Sette said.
The researchers found that virus-specific antibodies do persist in the bloodstream months after infection. Importantly, the body also has immune cells called memory B cells at the ready. If a person encounters SARS-CoV-2 again, these memory B cells could reactivate and produce SARS-CoV-2 antibodies to fight re-infection.
The SARS-CoV-2 virus uses its “spike” protein to initiate infection of human cells, so the researchers looked for memory B cells specific for the SARS-CoV-2 spike. They found that spike-specific memory B cells actually increased in the blood six months after infection.
“This implies that there’s a good chance people would have protective immunity, at least against serious disease, for that period of time, and probably well beyond that,” said Crotty.
The team cautions that protective immunity does vary dramatically from person to person. In fact, the researchers saw a 100-fold range in the magnitude of immune memory. People with a weak immune memory may be vulnerable to a case of recurrent Covid-19 in the future, or they may be more likely to infect others.
“There are some people that are way down at the bottom of how much immune memory they have, and maybe those people are a lot more susceptible to reinfection,” Crotty added.
“It looks like people who have been infected are going to have some degree of protective immunity against reinfection,” added Weiskopf. “How much protection remains to be established.”
The researchers will continue to analyse samples from Covid-19 patients in the coming months and hope to track their responses 12 to 18 months after the onset of symptoms.