Antibodies from original Covid virus strain don't bind to variants: Study

People infected with the original strain of the virus that causes Covid-19 early in the pandemic produced antibodies that don't bind well to newer variants, according to a study.

The finding, published in the journal Nature Communications, has implications for the ability of new variants to reinfect people who contracted earlier versions of the virus, as well as for the continuing efficacy of vaccines and the design of booster shots.

The researchers mined published papers about Covid-19 patients for data about the sequence of the antibodies they produced. They focused on antibodies against the spike protein, the part of the virus that binds to receptors on human cells to infect them.

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The spike protein is the target of most vaccines.

The team found that many antibody sequences converged into two main groups, indicating a consistent human immune response to the virus.

"We really focused on characterising the antibodies created in those infected with the original strain of the virus," said study first author Timothy Tan, a graduate student at the University of Illinois Urbana-Champaign, US.

"Before we started the study, variants weren't much of a problem. As they emerged, we wanted to see whether the common antibodies we identified were able to bind to newer variants," Tan said.

The researchers studied the convergent antibodies' ability to bind to several variants and found that they no longer bound to some.

When people make quite similar antibodies to a particular virus, it is called convergent antibody response.

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”Even though this antibody response is very common with the original strain, it doesn't really interact with variants," said study leader Nicholas Wu, a professor at the University of Illinois.

This raises the concern of the virus evolving to escape the body's main antibody response, the researchers said.

Some antibodies should still be effective -- the body makes antibodies to many parts of the virus, not only the spike protein -- but the particular groups of antibodies seen in the study will not be as effective, they said.

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The researchers said they would like to conduct similar studies characterising antibody response for Delta and other variants, to see whether they also produce a convergent response and how it differs from the original strain.

"We want to design vaccines and boosters, if needed, that can protect a majority of the population," Tan said.

"We expect that the antibody response to those variants would be quite different," he added.

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