Breakthrough infections among some fully vaccinated individuals may result in "super immunity" against Covid-19, according to a study published Thursday in JAMA.

Breakthrough infections may lead to 'super immunity'

For the study, researchers at Oregon Health & Science University (OHSU) compared blood samples from 52 OHSU employees who had received the Pfizer-BioNTech Covid-19 vaccine.

Among the 52 participants, OHSU Occupational Health testing identified 26 individuals with mild breakthrough infections following vaccination—with 10 confirmed cases of the delta variant, nine non-delta cases, and seven cases with unknown variants.

Researchers then measured the antibody levels in the blood samples of the breakthrough cases. They discovered that the antibodies in these samples were both more abundant and as much as 1,000% more effective than the antibodies generated two weeks after the second dose of the Pfizer-BioNTech vaccine, OHSU News reports.

According to the authors, the results of the study suggest the immune response triggered by breakthrough infections in fully vaccinated individuals could also be highly effective against other Covid-19 variants.

In addition, the findings suggest people may develop a stronger immune response with each subsequent exposure following vaccination—even after exposure to new variants.

"You can't get a better immune response than this," said Fikadu Tafesse, lead author of the study and assistant professor of molecular microbiology and immunology at the OHSU School of Medicine. "These vaccines are very effective against severe disease. Our study suggests that individuals who are vaccinated and then exposed to a breakthrough infection have super immunity."

'The key is to get vaccinated'

While multiple studies have shown that one dose of a vaccine following an initial Covid-19 infection offers protection against re-infection, "[t]his is one of the first that shows a breakthrough infection following vaccination generates stronger immunity than prior infection or vaccination alone," said Monica Gandhi, an infectious disease expert at the University of California, San Francisco.

According to Shane Crotty, a professor at the La Jolla Institute for Immunology in California, the findings demonstrate just how effective the immune system is—each time the immune system encounters the virus or the vaccine, it learns how to more effectively fight it.

"This is what the immune system evolved to do, to make guesses from something it's been exposed," Crotty said.

Currently, vaccine immunity is facing a real-world trial against the new omicron variant.

"We have not examined the omicron variant specifically, but based on the results of this study we would anticipate that breakthrough infections from the omicron variant will generate a similarly strong immune response among vaccinated people," Tafesse said.

As omicron continues to spread, these findings are "likely what the future will hold for most vaccinated individuals," Gandhi said.

"What we're saying is, we know life happens. If you happen to be exposed to the virus, you'll have this amazing immune response," Tafesse said. "It mirrors the immunity response we get to the booster."

"I think this speaks to an eventual end game," said co-author Marcel Curlin, associate professor of medicine in the OHSU School of Medicine who also serves as medical director of OHSU Occupational Health. "It doesn't mean we're at the end of the pandemic, but it points to where we're likely to land: Once you're vaccinated and then exposed to the virus, you're probably going to be reasonably well-protected from future variants."

"The key is to get vaccinated," Curlin said. "You've got to have a foundation of protection." (Weise, USA Today, 12/17; Robinson, OHSU News, 12/16; Bates et al., JAMA, 12/16)