The Centers for Disease Control and Prevention now advises that all Americans over 18 should get an additional dose of one of the approved Covid-19 vaccines, a stronger recommendation than its guidance in recent weeks. And the agency linked its update to the new variant.
Many experts also support boosting the entire population; others remain skeptical about whether the US should prioritize additional shots for all healthy adults, given that protection against serious illness and death from two shots appears to be holding up.
By and large, experts in both camps say omicron has not changed how they are thinking about booster shots — at least not yet.
First, while it’s too early to tell how vaccines will hold up against omicron, many experts doubt that a new formula to fight off the variant will be needed. Existing vaccines, plus the overall boost in antibodies from a booster shot for many people, could ultimately be enough.
“I don’t think we are going to need variant-specific boosters,” Monica Gandhi, professor of medicine at UC-San Francisco, told me. She pointed out the measles vaccine, which was developed in 1963, has never been updated.
Second, while we don’t know when or if omicron will become the dominant strain in the US, booster shots offer one benefit right now: They protect you against the version of the virus that is already dominant in the US right now, the delta variant. Cases have risen, immunity from shots in the spring may be waning, and the cold weather and the holidays are driving people inside.
The broader outlook, not fears of an omicron wave, is the most pressing reason to get a third shot, experts say.
Will we need an omicron-specific booster?
The omicron variant appears to have significant mutations compared to previous versions of the virus, which may make it more likely to overcome immunity from vaccines or prior infections. But it will take weeks for the data to come in on whether this is actually happening, and even more time to know what it would mean for people who are already vaccinated.
Several of the experts I spoke to suspected an omicron booster would not ultimately be necessary. “I think the more likely bet, like the other three variants, is this variant also will be protected against serious illness,” Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, told me.
The vaccines have already held up relatively well against the delta variant; there was some decline in vaccine effectiveness in protecting against any illness as delta became dominant over the summer, according to CDC studies. But the protection against severe illness — meaning hospitalization or death — remained strong for most people with the two-dose regimen. That is seen as evidence that the existing vaccines may perform strongly against omicron, too, even with its numerous mutations.
“The vaccines protected against the very recent surge caused by the delta variant, even though delta differs genetically from the vaccine strain,” Matthew Laurens, a professor with the Center for Vaccine Development and Global Health at the University of Maryland, told me.
The higher antibody response to the virus you have after a booster shot might also provide broad protection against different variants, including omicron.
“The recent results of booster studies for mRNA vaccines support that a third dose increases the antibody response to vaccination,” Laurens said, “and a higher antibody response likely will include more antibodies that are able to cross-protect against variant virus.”
The bottom line: While there’s still a lot we don’t know, current booster shots could be enough to do the trick against omicron, which is why the CDC is pressing ahead with urging all US adults get an additional dose.
“The recent emergence of the Omicron variant (B.1.1.529) further emphasizes the importance of vaccination, boosters, and prevention efforts needed to protect against COVID-19,” CDC Director Rochelle Walensky said in a statement accompanying the new guidelines.
The booster debate doesn’t necessarily change with omicron
There is still some disagreement among experts about whether booster shots are appropriate for everybody. The omicron variant may not change that debate.
The vast majority of experts agree that booster shots make sense for older and immunocompromised people, who do not receive the same protection from the two-dose regimen as the rest of the population. There has been less consensus about boosters for younger and healthy adults, though the CDC now recommends an additional dose for everyone over 18.
The skeptics point to the evidence that the vaccines remain strongly protective against severe symptoms for younger, healthier people, even if their effectiveness in preventing any illness has slipped. They worry about the risk of side effects, such as heart inflammation, for healthy people who may not benefit much from another dose.
“I don’t think we have enough data to say this vaccine isn’t doing what it’s supposed to be doing, which is protect against severe illness,” Offit told me. “This vaccine continues to do that. We sort of damn it by calling these mild illnesses breakthrough infections.”
They are also concerned that the booster drive could distract from the campaign to get shots to unvaccinated people, both in the US and the rest of the world. About 30 percent of the US population remains unvaccinated; 44 percent of the global population — 3.4 billion people — have not received a single dose of a Covid-19 vaccine.
There are biological reasons that immunity against any symptoms would fade but protection against serious illness would hold up. The human immune system has multiple layers of defense against outside invaders.
Antibodies can stamp out a virus before it ever develops into an infection — but they are also more likely to dwindle over time. Memory cells, on the other hand, can last for years and, though they activate more slowly, they can prevent symptoms from becoming too severe after an infection has already begun. In other words, while your immune system might not be as good at preventing you from getting sick at all, it still has the necessary tools to prevent a mild illness from developing to the point you have to go to the hospital.
“Most scientists believe we should still have protection against severe disease with vaccinations with the omicron variant,” Gandhi said. “If you want a burst of new antibodies against the virus to protect you from mild breakthroughs, the original vaccine’s booster should work to do that.”
Some of these skeptics have also argued the US needs to be more specific about what the booster campaign is supposed to achieve. Is it supposed to stop all illness? Or is it just supposed to help prevent the worst outcomes and make Covid-19 something we can live with?
But some people really don’t want to get sick at all.
“I got my shingles vaccine not because I thought I would die from shingles. I got it because I did not want to get shingles,” said Peter Hotez, co-director of the Texas Children’s Hospital Center for Vaccine Development. “That’s true of most adult vaccines.”
While the two-dose regimen has held up pretty well against the currently dominant delta variant, that has been evidence of some waning protection against severe illness. As Harvard Medical School’s Michael Klompas wrote in JAMA earlier this month, a number of ongoing investigations “suggest that there may be a parallel decrease in vaccine effectiveness against hospitalizations with the passage of more time.”
That would strengthen the case for boosters, and boosting can have other benefits as well. The vaccines appear to lead to less transmission and also reduce the chances of long Covid if the person does become infected with the virus.
Many experts are persuaded that the benefits of boosting most everybody outweigh the risks — a stance the CDC has now endorsed too.
“The evidence for boosters is pretty compelling, and is in response to concerns about waning immunity against the current strains of the virus we are already living with,” Jen Kates, director of global health and HIV policy at the Kaiser Family Foundation, told me. “Delta is still the dominant variant in the US and that should be the primary concern for anyone.”