Up to 99 million Americans are now eligible for a COVID-19 vaccine booster shot, after the Centers for Disease Control and Prevention last week signed off on sweeping new for recipients of Pfizer, Moderna and Johnson & Johnson's vaccines.
Those recommendations came after the Food and Drug Administration updated their emergency use authorizations to allow boosters for all three vaccines. The FDA is also allowing eligible Americans to mix-and-match their booster shots, which means you can choose to receive an additional dose from any of the three brands that are available.
Here's what we know so far:
Johnson & Johnson recipients
That comes after the FDA concluded that even the highest estimates of the single-shot vaccine's protection were "consistently less" than the mRNA-based vaccines from Pfizer or Moderna.
Data presented to the FDA's outside vaccine advisers by Johnson & Johnson says vaccine effectiveness against symptomatic COVID-19 climbed to 94% in the U.S. after a booster shot. A group of the CDC's vaccine advisers also concluded that the risks of rare but serious side effects following a second dose of the vaccine were "unlikely to be greater" than after the first dose.
However, some of the agency's outside vaccine advisers said they would probably counsel their patients at higher risk of a rare blood clotting side effect linked to the Janssen vaccine to opt for a dose of Pfizer or Moderna instead.
Out of more than 15 million recipients in the U.S. of Johnson & Johnson's vaccine, the CDC and FDA have confirmed close to 50 reports of the condition known as thrombosis with thrombocytopenia syndrome. Most were women under 50 years old.
"I was personally not going to recommend a booster dose of the same product of Janssen, so I'm glad that we have included the mix-and-match," Dr. Pablo Sanchez, one of the CDC's vaccine advisers, said last week at the committee's meeting to discuss booster shots.
Pfizer and Moderna recipients
Currently, all seniors 65 and older who received Pfizer or Moderna's COVID-19 vaccines are recommended to get a booster shot at least six months after they were first vaccinated.
The CDC also expanded eligibility for adults ages 18 and up who were vaccinated six months ago if they live in "long-term care settings," have "underlying medical conditions," or are working or living in "high-risk settings" like prisons, hospitals or homeless shelters. People at higher risk of exposure from their jobs — including teachers and school support staff, grocery clerks, postal workers, factory workers, public transit crews, police and first responders, and others — are also eligible.
Like with earlier booster shot recommendations for, most pharmacies and providers are relying only on people's "self-attestation" and not requiring proof of eligibility for the additional shots.
FDA and CDC officials say they could further expand eligibility for booster shots soon as authorities gather more data on the need and potential risks.
"There is evidence to suggest potentially that lowering the age of those eligible for boosters may make sense in the future. Something we're looking at closely," Dr. Peter Marks, the FDA's top vaccines official, told reporters last week.
Those risks include myocarditis and pericarditis, rare heart side effects linked to the mRNA-based Pfizer and Moderna vaccines that have occurred mostly in young males. These cases have been mostly mild and typically resolve within a day, according to federal health officials, but often require hospitalization.
Data presented to the CDC's outside vaccine advisers last week suggested the risk of myocarditis could be "slightly increased" in adults under 30 after Moderna's first two doses compared to Pfizer's.
However, some experts hope Moderna's decision to halve the size of its booster dose — 50 micrograms instead of the 100 micrograms of its first two shots — could cut the risk of myocarditis after the booster.
Data from Pfizer's booster rollout in Israel, which was presented to the FDA's vaccine advisers earlier this month, also suggests the risk of myocarditis was lower after the third dose while effectively curbing a surge in COVID-19 cases there.
"We may well get there. It's a matter of having the data, and ensuring that when we make that decision, the benefits clearly outweigh the risks throughout the population," Marks said.
The FDA's decision to allow for mixing-and-matching booster shots was based in part on early data from trials led by the National Institutes of Health which suggest all combinations of so-called "heterologous" boosting are safe and effective at increasing protection.
Federal health officials also pointed to situations that made requirements to match booster shot brands tricky, like when people do not remember which shots they were first vaccinated with, had a bad reaction to their initial vaccinations, or do not have access to the same brand at their nearby pharmacies.
So far, the FDA's scientists concluded there is not enough data from the NIH's trial to pick a "preferred strategy" for boosting. The study's scientists had cautioned that their trial was not designed to "directly compare" the immune response triggered by different booster combinations.
"We will not articulate a preference. My understanding is that most people will have done largely well with the initial vaccine that they got and may express a preference, very much, for the original vaccine series they got, having done very well," CDC Director Rochelle Walensky told reporters last week.
"There may be some people who might prefer another vaccine over the one that they received, and the current CDC recommendations now make that possible."
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