Cristina Licup receives her COVID-19 booster shot where she works at the Hebrew Home at Riverdale in New York, Sept. 27, 2021. Credit: Seth Wenig / AP

COVID-19 booster shots from Pfizer Inc. and Moderna Inc. received unanimous backing for use in all U.S. adults from public health advisers, clearing the way for millions to gain additional protection before the threat of a winter surge.

All 11 advisers to the Centers for Disease Control and Prevention voted in favor of third doses for people 18 and older just hours after they were cleared Friday by U.S. regulators. The committee also voted to recommend that people age 50 and older should receive the boosters. CDC Director Rochelle Walensky still must sign off on the recommendation from the agency’s Advisory Committee on Immunization Practices before vaccinations begin.

Booster shots of messenger RNA vaccines have been available for people 65 and over along with others at higher risk of severe disease since mid-September. Under Food and Drug Administration guidelines, any of the three authorized shots — including one from Johnson & Johnson — can be used as a booster, regardless of which vaccine a person received initially.

However, at least nine states are already offering booster shots to all adults, going beyond federal guidance and reigniting the national debate on eligibility for the supplemental doses. The patchwork of state and federal guidelines may be standing in the way of some people getting vaccinated. Four in 10 vaccinated adults are unsure whether they are eligible for a booster, according to an October survey by the Kaiser Family Foundation.

“Individuals who are right now absolutely eligible for boosters may not be able to parse the guidelines,” said Nirav Shah, director of the Maine Center for Disease Control and Prevention and president of the Association of State and Territorial Health Officials, at the advisory panel meeting. “Our concern is eligible individuals are not receiving boosters right now because of this confusion.”

The guidelines may have only served to further roil what’s already been a contentious vaccine campaign, according to Walid Gellad, director of the University of Pittsburgh’s Center for Pharmaceutical Policy and Prescribing.

“We have been very careful this entire rollout of vaccines and therapeutics to make sure we follow the science and abide by the scientific deliberations of groups like FDA and CDC,” he said in an interview. “What is happening now — with governors deciding on their own to expand access to a therapy beyond what FDA and CDC intended — is troubling and not what we should be applauding.”

The Biden administration has been eager to use vaccines to keep the pandemic at bay and maintain economic and educational activity. Shots have been cleared for children as young as 5.

However, data from drugmakers and researchers indicates that the effect of the initial two-shot regimes from Moderna and the partnership of Pfizer and BioNTech SE is fading. Surveillance also shows that COVID immunity can be restored with boosters.

So far, of 195 million fully vaccinated Americans, about 32 million have received a booster shot. While a wider recommendation may simplify health messages for the public, it may be interpreted by some in unintended ways, said Monica Gandhi, an infectious disease expert at the University of California, San Francisco.

“I am very worried that this decision to approve boosters for everyone will make the unvaccinated question the effectiveness of the vaccines,” Gandhi said in an interview.

Some experts have been cautious about expanding the use of boosters in younger people. Advisers to the CDC and FDA have discussed whether that may put more people at risk of myocarditis, an inflammation of heart tissue.

Fiona Rutherford, Bloomberg News