Repeat Covid-19 shots help ward off variants, even other viruses

Some scientists have worried that the success of the first vaccines may undermine the utility of annual updates, much as the annual flu shot can interfere with immune responses in subsequent years, but a new study shows that Covid-19 vaccines don’t do that, and actually “promote the development of broadly inhibitory antibodies,” says a news release from Washington University School of Medicine in St. Louis, where the study was conducted.

Everyone who is 65 and over, or has medical conditions that make them more vulnerable, is advised to get a Covid-19 booster this spring.

The study, available online in the peer-reviewed scientific journal Nature, shows that people repeatedly vaccinated for Covid-19 — initially getting shots aimed at the original SARS-CoV-2 variant, followed by boosters and updated vaccines targeting variants — generated antibodies capable of neutralizing a wide range of virus variants and even some distantly related coronaviruses.

“The findings suggest that periodic re-vaccination for Covid-19, far from hindering the body’s ability to recognize and respond to new variants, may instead cause people to gradually build up a stock of broadly neutralizing antibodies that protect them from emerging SARS-CoV-2 variants and some other coronavirus species as well, even ones that have not yet emerged to infect humans,” the release says.

“The first vaccine an individual receives induces a strong primary immune response that shapes responses to subsequent infection and vaccination, an effect known as imprinting,” said Dr. Michael S. Diamond, senior author of the study. “In principle, imprinting can be positive, negative or neutral. In this case, we see strong imprinting that is positive, because it’s coupled to the development of cross-reactive neutralizing antibodies with remarkable breadth of activity.”

Imprinting is the natural result of how immune-system memory works. A first vaccination triggers the development of memory immune cells. When people receive a second vaccination quite similar to the first, it reactivates memory cells elicited by the first vaccine. These memory cells dominate and shape the immune response to the subsequent vaccine.

The study suggests that regular re-vaccination with updated Covid-19 vaccines against variants might give people the tools to fight off not only the variants represented in the vaccines, but also other variants and related coronaviruses, possibly including ones that have not yet emerged.

“At the start of the Covid-19 pandemic, the world population was immunologically naïve, which is part of the reason the virus was able to spread so fast and do so much damage,” said Diamond, a professor of molecular microbiology, pathology and immunology. “We do not know for certain whether getting an updated Covid-19 vaccine every year would protect people against emerging coronaviruses, but it’s plausible. These data suggest that if these cross-reactive antibodies do not rapidly wane — we would need to follow their levels over time to know for certain — they may confer some or even substantial protection against a pandemic caused by a related coronavirus.”