In-Depth: Should you still get a booster after a breakthrough infection?

Breakthrough Infection vs Hybrid Immunity
Posted at 6:06 PM, Oct 22, 2021
and last updated 2021-10-22 21:12:56-04

SAN DIEGO (KGTV) -- There are no official guidelines from the Centers for Disease Control and Prevention on whether fully vaccinated people who have also recovered from a COVID infection need a booster.

Experts say most people with so-called hybrid immunity likely do not need a booster, but the additional dose might be helpful, especially for those at high risk.

Hybrid immunity is when someone recovers from a COVID infection before getting vaccinated. It typically results in antibody levels that are 25 times higher than vaccination alone and 100 times higher than infection alone, according to a paper in Science.

Scientists are still studying how the immune system reacts to a breakthrough infection, which is when a fully vaccinated person later gets infected.

“It may very well be that the breakthrough infection has acted as its own booster if you wish, but we don’t know that,” said Dr. Alessandro Sette, a professor at the La Jolla Institute for Immunology whose lab has published several studies on the immune response to COVID.

Sette said his lab is still studying the question, but a draft of a study released Thursday might offer an early clue. Researchers from Harvard and MIT examined the immune systems of 35 people who had breakthrough infections during the Provincetown, Mass. outbreak.

They found a breakthrough infection increased neutralizing antibody levels against the delta variant by 34-fold. That’s a larger increase than the typical third dose, which ranges from five-fold to 17-fold, according to an NIH-funded study.

Still, Dr. Sette cautioned there are theoretical reasons why a breakthrough infection might behave differently than hybrid immunity.

“It could be that someone that has breakthrough infection didn’t have as good of a strong immune response in the first place,” he said.

The interval between the breakthrough infection and the initial vaccination might also influence the strength of the immune response, Sette theorized. Several studies have shown that a longer interval between a two-dose vaccine results in stronger protection. A breakthrough soon after vaccination might not rev up the immune response.

Sette also worries that some people who suspect they had COVID, but never confirmed it through testing, might avoid getting a booster. That would be a very dangerous situation," he said.

With more studies underway, doctors say people with a breakthrough infection should follow the same booster recommendations as everyone else.