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The question of who can or should get booster doses of coronavirus vaccines is much simpler now.

The US Centers for Disease Control and Prevention and the US Food and Drug Administration have okayed boosters for every adult who got Moderna’s or Pfizer/BioNTech’s Covid-19 vaccine six months ago or longer.

The agencies had already said everyone who got Johnson & Johnson’s Janssen vaccine two months ago or more should get a booster. Friday’s decision means everyone 18 and older who is fully vaccinated should consider getting another dose of vaccine.

Previous guidance was more complicated and CDC vaccine advisers expressed relief at the idea that the advice would be more streamlined.

“The current guidelines, so well intentioned and thoughtful, generate an obstacle to uptake of boosters. In pursuit of precision, they create confusion,” Dr. Nirav Shah, president of the Association of State and Territorial Health Officials (ASTHO) and director of Maine’s Center for Disease Control and Prevention, told Friday’s meeting of CDC vaccine advisers before they voted to recommend broader guidelines.

“Our concern is that eligible individuals are not receiving boosters right now because of this confusion.”


Anyone who’s at least 18 and was fully vaccinated at least six months ago. For those who got Pfizer’s or Moderna’s vaccine, that means two doses.

The CDC and FDA had already recommended that anyone who got Johnson & Johnson’s Janssen one-shot vaccine two months ago or longer should get a booster dose.

In most cases, people should be able to get a free booster vaccine by showing a CDC vaccination card.


The authorization to mix and match vaccines still applies, so it doesn’t matter. People who got two doses of Pfizer vaccine may either get a third dose of the Pfizer/BioNTech vaccine, or they may opt for a Moderna booster, which is a half-sized dose of the regular Moderna dose, or they can get a Johnson & Johnson booster.

The same goes for all the vaccines. Plus, people who got a vaccine that has not been authorized in the US – for example, an AstraZeneca vaccine in Europe or the Caribbean—may get a booster dose of Pfizer’s vaccine in the US.

Studies show that any of the three vaccines, given as boosters, bump people’s immunity back up to levels provided after the second dose. For the J&J vaccine, a booster makes immunity stronger than it was after the first dose.

Data presented to CDC’s vaccine advisers Friday showed booster shots of either Moderna’s or Pfizer’s vaccine were safe, caused no worrying side-effects, and revved up people’s immune responses regardless of age.

One consistent pattern: Moderna’s booster caused more immediate reactions such as sore arms, fatigue and headaches. Even at the half-sized booster dose, Moderna’s product delivers more vaccine than Pfizer’s full-sized dose does – 50 micrograms versus 30 micrograms – and doctors say it’s possible that accounts for the difference. But there were no concerning safety reports from either, according to CDC vaccine safety specialists.


As with the second dose of vaccine, doctors say it takes two weeks for immunity to peak. So the CDC is recommending that people get their boosters as soon as possible.

People who have not received boosters yet won’t be able to get one in time to achieve peak renewed immunity before Thanksgiving, but other holidays are coming and the prospect of winter travel has officials worried.


The biggest risks from waning immunity are to older adults – especially those 65 and older. That’s why the FDA and CDC acted first for that age group, as well as for people otherwise at risk of severe disease, such as those with medical conditions, even if they are younger.

The companies that make the vaccines have not reported any evidence that people 18 and under who got vaccinated are suffering from waning immunity or breakthrough infections yet. These younger age groups are less at risk of severe disease overall, and there’s less of a concern about the danger to them from breakthrough infections.

Pfizer’s vaccine was authorized for children as young as 12 in May, which would put some children that age at the six-month mark. But the CDC and FDA are far more concerned about getting boosters to adults first – and, most important, getting the first shots into the millions of adults and children who are authorized to be vaccinated but who haven’t been yet.


Not in the United States. The CDC defines a fully vaccinated person as someone two weeks after having received two doses of the Pfizer/BioNTech vaccine at least three weeks apart, two doses of Moderna’s vaccine four weeks apart or a single dose of the Johnson & Johnson vaccine. That hasn’t changed.

At least two governors – New Mexico’s Michelle Lujan Grisham and Connecticut’s Ned Lamont, both Democrats, have said they don’t consider people fully vaccinated unless they’ve had a booster, but so far those are opinions, not policies.


It’s too soon to say. It’s possible that as with vaccines like the MMR (measles, mumps and rubella) vaccine, once the initial few doses are out of the way, people can count on being immune for life.

Doctors hope that boosting six months after the initial dose will provide much longer-lasting immunity than giving two quick doses a few weeks apart – even as they agree that was 100% the right approach for a new vaccine being used at the start of a pandemic.

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It’s also too soon to know whether immunity might wane after months or years. And it’s too soon to know if a new variant might emerge and spread that evades the protection offered by a vaccine and, as with flu vaccines every year, the formula may have to be tweaked protect against the changed virus.