Immunity to COVID-19 may persist six months or more

Immunity to COVID-19 may persist six months or more

After people with COVID-19 have largely recovered, immune proteins called antibodies are still detectable six months later. What’s more, the proteins have sharpened their skills at fighting the coronavirus, researchers report in a preliminary study posted November 5 at bioRxiv.org. Leftover pieces of the virus remaining in the gut after symptoms have disappeared may help the immune system work to refine that response.

The finding also bodes well for how long a vaccination might provide protection. Immunity from a vaccine is expected to last as long or longer than natural immunity.

Antibodies, which are immune proteins that bind to microbes to fight off an infection, are part of the body’s cache of immune defenses. People typically make a wide variety of antibodies during an infection. These proteins can recognize different surfaces on viruses — like a Swiss Army knife able to work on various parts of the virus — and evolve over time to better recognize their target (SN: 4/28/20).

Six months after an infection with the coronavirus that causes COVID-19, called SARS-CoV-2, people appear to have built an arsenal of antibodies that are not only more potent than the ones developed early on, similar to what has been seen in other infections. Those antibodies can also recognize mutated versions of the virus, researchers found. In addition to antibody upgrades, long-lasting immune cells that make antibodies, called memory B cells, stick around in the blood, poised to launch a rapid response should people be exposed to the virus again.

“The main message is that the immune response persists,” says Julio Lorenzi, a viral immunologist at the Rockefeller University in New York City. “We see these B cells surviving over time and the antibodies six months after infection are even better than the beginning of the infection.”

In the study, Lorenzi and colleagues analyzed the antibodies that 87 people made against the coronavirus at one and six months after developing symptoms. Although antibody levels in the blood waned, the immune proteins were still detectable after six months. Importantly, levels of memory B cells were stable, an assessment of 21 of the 87 participants showed — a sign that those cells may remain in the body for a while.

Other studies have hinted that B cells can persist for more than six months in recovered COVID-19 patients. Preliminary results of one study uncovered that memory B cells — as well as other cells involved in immune memory known as T cells — decline slowly in the blood, researchers reported November 16 at bioRxiv.org. That slow decrease could mean that immunity might last for years, at least in some people (SN: 10/19/20).

What’s more, Lorenzi and his team found, B cells refined the antibodies they made over a five-month time span to generate proteins that are better at recognizing the coronavirus. In an analysis of cells from six people, the researchers discovered changes in the genetic instructions that B cells use to make antibodies, a sign that the B cells were making new variations. 

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