Researchers who are learning more about how a COVID-19 booster shot works after initial vaccination against the coronavirus have new insight into various levels of protection.
Protection against an infection is less durable than the longer-lasting protection against serious outcomes from severe disease.
“There’s mounting evidence that that’s a durable level of immunity — that we’re protected against severe disease for a long time, meaning months, possibly years,” said Dr. Stuart C. Ray, a professor of medicine and infectious diseases at Johns Hopkins Hospital who was not involved in the studies.
“The duration of that immunity against reinfection doesn’t stay for a long time, but the protection against severe infection lasts for a long time.”
Protection against infection that would be evident from a positive PCR test can begin dropping in as few as three months.
People with compromised immune systems or people of advanced age tend not to get as much immunity, and immunity doesn’t last as long as with people who have healthier immune systems.
“We see that dropping down after anywhere from three to six months, depending on the person — there’s a lot of variability. … Especially with the new variants like omicron, we saw that protection against infection dropping down within four to six months,” Ray said.
Noting that the coronavirus isn’t going away, Ray said it’s important to protect the most vulnerable by getting as many people as possible vaccinated.
“What we can hope to do is lower the level of spread so that new variants don’t evolve, and get enough people vaccinated or immune otherwise, so that we can prevent severe disease from overwhelming our health care system,” he said.
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