Are Vaccines Fueling New Covid Variants?

Public-health experts are sounding the alarm about a new Omicron variant dubbed XBB that is rapidly spreading across the Northeast U.S. Some studies suggest it is as different from the original Covid strain from Wuhan as the 2003 SARS virus. Should Americans be worried?

It isn’t clear that XBB is any more lethal than other variants, but its mutations enable it to evade antibodies from prior infection and vaccines as well as existing monoclonal antibody treatments. Growing evidence also suggests that repeated vaccinations may make people more susceptible to XBB and could be fueling the virus’s rapid evolution.

Prior to Omicron’s emergence in November 2021, there were only four variants of concern: Alpha, Beta, Delta and Gamma. Only Alpha and Delta caused surges of infections globally. But Omicron has begotten numerous descendents, many of which have popped up in different regions of the world curiously bearing some of the same mutations.

“Such rapid and simultaneous emergence of multiple variants with enormous growth advantages is unprecedented,” a Dec. 19 study in the journal Nature notes. Under selective evolutionary pressures, the virus appears to have developed mutations that enable it to transmit more easily and escape antibodies elicited by vaccines and prior infection.

The same study posits that immune imprinting may be contributing to the viral evolution. Vaccines do a good job of training the immune system to remember and knock out the original Wuhan variant. But when new and markedly different strains come along, the immune system responds less effectively.

Bivalent vaccines that target the Wuhan and BA.5 variants (or breakthrough infections with the latter) prompt the immune system to produce antibodies that target viral regions the two strains have in common. In Darwinian terms, mutations that allow the virus to evade common antibodies win out—they make it “fitter.”

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