What immunity to COVID-19 really means

Immunity to seasonal coronaviruses (such as those that cause common colds), for example, starts declining a couple of weeks after infection. And within a year, some people are vulnerable to reinfection. That observation is disconcerting when experts say it is unlikely we will have a vaccine for COVID-19 within 18 months. But studies of SARS-CoV—the virus that causes severe acute respiratory syndrome, or SARS, which shares a considerable amount of its genetic material with SARS-CoV-2—are more promising. Antibody testing shows SARS-CoV immunity peaks at around four months and offers protection for roughly two to three years. As Preeti Malani, chief health officer and a professor of medicine at the University of Michigan, said in a video interview with JAMA Editor in Chief Howard Bauchner,this period presents “a pretty good time line for thinking about vaccines and therapeutics” for COVID-19.

Even if the antibodies stick around in the body, however, it is not yet certain that they will prevent future infection. What we want, Bowdish says, are neutralizing antibodies. These are the proteins that reduce and prevent infection by binding to the part of a virus that connects to and “unlocks” host cells. They are relatively easy to detect, and they are far easier for vaccine developers to generate than the alternative: the immune system’s T cells. In contrast, nonneutralizing antibodies still recognize parts of the pathogen, but they do not bind effectively and so do not prevent it from invading cells.

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