Waning COVID-19 Vaccine Immunity: Here's What We Know

by Elizabeth Broadbent
Originally Published: 

On November 19, the director of the Centers for Disease Control signed off on the Food and Drug Administration’s recommendation to expand eligibility for COVID-19 booster shots to all American adults who had received a dose of the Pfizer/BioTech or Moderna vaccines at least six months earlier. Those who got jabbed with Johnson & Johnson vaccines, always the odd ones out, had already been authorized for a booster two months after their initial vaccination. These recommendations for booster shots come as more information creeps out about waning vaccine immunity: both scientific studies and rising infection rates.

“Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays,” says CDC director Rochelle Walensky.

Here’s the fine print (please read aloud as fast as possible): While the CDC didn’t proclaim that everyone 18-49 needed a booster, the agency said they could get one they choose, and people 50-64 “should get a booster.” Previously, they had only recommended boosters for those in that age group with underlying medical conditions. The CDC had already said that those over 64 should get a COVID-19 booster, regardless of health status.

So why do we need boosters all of a sudden?

Well, waning vaccine immunity.

Pause for collective explosion of expletives.

Waning Vaccine Immunity?

“Waning vaccine immunity” refers to how a vaccine becomes less effective at fighting a disease over time. The Pfizer vaccine is 90% effective against symptomatic infection just after a second dose of the vaccine. According to an English study, twenty weeks after that second dose, its efficacy at preventing symptomatic infection has dropped to 70%. Moderna’s protection also drops over time. And while US and Canadian studies differ about how much Pfizer and Moderna’s efficacy rates decline over time against the Delta variant in particular, they do decline — the US study showed Pfizer’s protection dropping precipitously to just over 50% less than 20 weeks out.

Ouch, Pfizer. 50%? I got Moderna and a booster, or that study might have me hiding from the mailman.

But here’s the good news, which we so desperately needed. Both the Canadian and English studies showed that Pfizer and Moderna seem to maintain decent efficacy at preventing severe disease and hospitalization from COVID. So while we still have waning vaccine immunity, it’s not quite as dire as it seems. Yes, we have more cases of COVID. Yes, we have a few more severe cases of COVID. However: even without a booster, your vaccine has not stopped working.

Keep in mind: the goal of a COVID vaccine was never to keep you from getting COVID. You don’t get a COVID vaccine so you don’t get COVID. You get a COVID vaccine so you don’t get severe COVID and keel over. “The main objective of the COVID vaccine is to prevent severe disease and death, and they are still doing a good job at that,” said Melissa Higdon, a faculty member at the Johns Hopkins Bloomberg School of Public Health.

But What’s This Mean For The Winter?

Well, waning vaccine immunity is never good. Now we not only have to contend with the unvaccinated hordes, we have to deal with those who don’t think they need a booster — and who get COVID, then keep it flowing through said unvaccinated hordes. Dr. Anthony Fauci says that waning vaccine immunity, combined with the notorious Delta variant, could cause a “double whammy” impacting “even vaccinated people.”

“You’re going to see breakthrough infections, even more so than we see now among the vaccinated,” he said.


We’re moving into a perfect storm of a holiday season: people with waning vaccine immunity mixing with diehard antivaxxers, all sharing a table with only partially vaccinated children. None of these people are wearing masks, because all of them are snarfing turkey. Already, cases are surging to 80,000 a day, which ABC calls the highest in a month. Total hospitalizations have shot up for the first time in ten weeks, and 40 states are showing high transmission already.

So we have to keep selling the vaccine in the first place — convincing those who are still unconvinced that they need a COVID shot to begin with. Then we have to convince those who have already been convinced. Again. Combating COVID this winter will depend on “how well we implement a booster program,” says Fauci.

Three Vaxxes Could Become Standard

Fauci says that he thinks eventually, we won’t think of a booster shot as a booster, but as a standard part of our vaccine regime. “I happen to believe as an immunologist and infectious disease person, that a third shot boost for an mRNA is likely — should be part of the actual standard regimen, where a booster isn’t a luxury; a booster isn’t an add on; and a booster is part of what the original regimen should be — so that when we look back on this, we’re going to see that boosters are essential for an optimal vaccine regimen,” Fauci said.

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