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People infected with the original strain of the SARS-CoV2 virus that caused Covid-19 early during the pandemic outbreak produced a consistent antibody response, making two main groups of antibodies to bind to the spike protein on the virus's outer surface.

However, those antibodies don't bind well to newer variants, finds a new study, published in the journal Nature Communications.

According to researcher Nicholas Wu from the University of Illinois at Urbana-Champaign, characterising what kinds of antibodies the body is most likely to make to fight a natural infection is an important roadmap for vaccine design.

For the study, 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. The spike protein is the target of most vaccines.

They 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 Timothy Tan, a graduate student part of the research.

"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 added.

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

The finding 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 possible vaccine boosters.

"Even though this antibody response is very common with the original strain, it doesn't really interact with variants," Wu said.

"That, of course, raises the concern of the virus evolving to escape the body's main antibody response. 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 that we saw in this study will not be as effective," Wu added.

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