Covid boosters continue to protect most people for many months, perhaps years

According to a flurry of new studies, it looks as if Covid boosters will continue to protect most people from serious illness and death for many months, and perhaps even years — which means we probably won’t need to line up for another shot anytime soon.

Previous studies have shown that antibodies, the body’s first line of defense against the virus, can wane over time, leading some to worry that we may be stuck in an indefinite cycle of boosters. But Apoorva Mandavilli says that antibodies were just part of the picture.

“People are obsessed with antibodies,” Apoorva said, in part because antibodies are relatively easy and fast to study. “But antibody levels always go down, and that does not necessarily mean that immunity to severe illness is waning. That’s a bad way to think about your immune system.”

Instead, the new research looked at other parts of the immune system that can remember and destroy the virus, including B cells and T cells. The studies found that this diverse repertoire of defenses should be able to protect people who have had three shots, or even two, for months or years.

“Think of antibodies like the frontline soldiers, the very first ones that are standing guard at the gates and preventing enemies from getting in,” Apoorva said. Over time, if your body doesn’t see any new enemies, there may be fewer of these guards at the gate.

“But let’s say that you have very few antibodies and the virus does get in, then you have these backup defenses,” Apoorva said. “The B cells make more antibodies and the T cells can destroy any cell that is infected, so between them, they can basically put a stop to the infection and stop you from getting sick.”

This dual punch of T and B cells helps explain why many people who received two or even three doses of the vaccine could still be infected with the Omicron variant but only a small percentage became seriously ill. And two of the recent studies show that a third mRNA shot produces a wider variety of antibodies and a richer pool of B cells, explaining why the boosted see better results.

The T cells produced by four Covid vaccines — Pfizer, Moderna, Johnson & Johnson and Novavax — are about 80 percent as powerful against Omicron as they are against other variants, according to the new research. Given how different Omicron’s mutations are from previous variants, it’s very likely that T cells would mount a similarly robust attack on any future variant as well, researchers said.

This matches what scientists have found for the SARS coronavirus, which killed nearly 800 people in a 2003 epidemic in Asia. In people exposed to that virus, T cells have lasted more than 17 years. So far, experts said, the evidence indicates that long-term memory cells for the coronavirus may also linger over time.

“The vaccines are really excellent at producing long-term memory,” Apoorva said. “And if what we’re worried about is preventing our health care system from getting overwhelmed with a lot of sick people, those who already have had two doses and maybe three doses are good to go for at least a while.”