People infected with the original strain of the coronavirus that caused COVID-19 early in the pandemic 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, a new study has shown.

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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 that were developed to fight the original strain  and the design of possible vaccine boosters.

Characterising what kinds of antibodies the body is most likely to make to fight a natural infection is an important roadmap for vaccine design, said researchers from the University of Illinois Urbana-Champaign. "Antibody response is quite relevant to everything from understanding natural infection and how we recover from infection to vaccine design. The body has the capability to produce diverse antibody responses it's estimated we could make a trillion different antibodies. So when you see people are making quite similar antibodies to a particular virus, we call it a convergent antibody response," said Nicholas Wu, Professor of biochemistry at the varsity.

"That means we can design vaccines trying to elicit this kind of antibody response, and that is probably going to improve the responsiveness of more individuals to the vaccine," he added. The researchers searched 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, said graduate student Timothy Tan. The researchers studied the convergent antibodies' ability to bind to several variants and found that they no longer bound to some.

The team noted they would like to conduct similar studies characterising antibody responses to delta and other variants, to see whether they also produce a convergent response and how it differs from the original strain.