By Maggie Fox, Oct. 21 (CNN): The US Food and Drug Administration authorized booster doses of Covid-19 vaccines made by Moderna and Johnson & Johnson Wednesday and also said any of the three authorized vaccines could be used as a booster in a "mix and match" approach.
But it left in place a complex formula for who should get boosters and when with officials saying they may simplify the framework as more safety data comes in.
Now vaccine advisers to the US Centers for Disease Control and Prevention will consider the FDA's authorization, and offer their own advice. If CDC director Dr Rochelle Walensky signs off, people could start getting Moderna and J&J boosters within days.
The FDA gave emergency use authorization for a half dose of Moderna's vaccine as a booster for people fully vaccinated at least six months ago who are also at least 65, or who are at least 18 and at high risk of severe Covid-19 or have frequent institutional or occupational exposure to the virus.
It also authorized booster doses of Johnson & Johnson's vaccine for anyone who got that vaccine, so those 18 and older, at least two months ago.
And it said any of the three authorized vaccines could be used to boost. Pfizer already has authorization for booster shots for its vaccine for people vaccinated at least six months ago -- with the same restrictions as those for Moderna's vaccine: those 65 and older and those with a higher risk of severe disease.
"As the pandemic continues to impact the country, science has shown that vaccination continues to be the safest and most effective way to prevent COVID-19, including the most serious consequences of the disease, such as hospitalization and death," FDA Acting Commissioner Dr. Janet Woodcock said in a statement.
"The available data suggest waning immunity in some populations who are fully vaccinated. The availability of these authorized boosters is important for continued protection against COVID-19 disease."
Dr Peter Marks, director of the FDA's vaccine arm, the Center for Biologics Evaluation and Research, said the ability to use any authorized vaccine as a booster will simplify matters for people.
"Being able to interchange these vaccines is a good thing. It's like what we do with flu vaccines. Most people don't know what brand flu vaccine they received," Marks told reporters in a telephone briefing.
Marks said the FDA would consider lowering the age ranges for booster shots as more safety data comes in.
"We want to make sure that if we deploy the boosters in all of the age ranges, that we truly are making a benefit outweigh any risks," Marks said. "We will not hesitate to drop this age range as we see this benefit outweigh the risk, and because of the EUA authority that we have, we can do that in a relatively quick amount of time."
The CDC's vaccine advisers, the Advisory Committee on Immunization Practices, meet Thursday to decide on whether to recommend the FDA's authorization for the American people and then the CDC director will decide whether to sign off on ACIP's guidance.
The FDA said it decided to allow the mix-and-match boosters after National Institutes of Health researchers presented their findings last week to its vaccine advisers. Although the findings were limited, they made it clear mixing up the different vaccines was safe.
The agency gave some examples of how this might work.
"For example, Janssen COVID-19 Vaccine recipients 18 years of age and older may receive a single booster dose of Janssen COVID-19 Vaccine, Moderna COVID-19 Vaccine (half dose) or Pfizer-BioNTech COVID-19 Vaccine at least two months after receiving their Janssen COVID-19 Vaccine primary vaccination," it said.
"In another example, Moderna COVID-19 Vaccine and Pfizer-BioNTech COVID-19 vaccine recipients falling into one of the authorized categories for boosters (65 years of age and older, 18 through 64 years of age at high-risk of severe COVID-19, and 18 through 64 years of age with frequent institutional or occupational exposure to SARS-CoV-2) may receive a booster dose of Moderna COVID-19 Vaccine (half dose), Pfizer-BioNTech COVID-19 Vaccine or Janssen COVID-19 Vaccine at least six months after completing their primary vaccination," it added.
The instructions are confusing, said Dr. David Dowdy, an infectious diseases epidemiologist at the Johns Hopkins Bloomberg School of Public Health.
"It is hard for the average person to navigate all this and figure out what the right thing to do is," Dowdy told CNN.
Dowdy said he hoped the CDC would provide clearer guidance to the public about boosters. But he also said the emphasis on boosters was distracting the public from the bigger need to vaccinate more people in the first place.
"The pressure to get these recommendations out so quickly is coming from the public, is coming from the pharmaceutical companies. It is not coming from the virus," he said.
The initial two doses of Pfizer's or Moderna's vaccines are highly effective at preventing severe disease, Dowdy noted. "If you are a little confused by this -- it's not the worst thing in the world to wait a little bit as long as you've gotten that first series of vaccines," he said.