WASHINGTON (AP) — A panel of U.S. health advisers endorsed booster doses of Johnson & Johnson’s single-shot COVID-19 vaccine Friday, saying they should be offered at least two months after immunization.

J&J has asked the Food and Drug Administration for flexibility with its booster, arguing the extra dose adds important protection as early as two months after initial vaccination — but that it might work better if people wait until six months later.

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The FDA’s advisory panel voted unanimously that a booster should be offered without setting a firm time. The advisers cited growing worry that recipients of J&J’s vaccination seem to be less protected than people who got two-dose Pfizer or Moderna options — and that most got that single dose many months ago.

The FDA isn’t bound by the vote but its ultimate decision could help expand the nation’s booster campaign.

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The government says all three U.S. vaccines continue to offer strong protection against hospitalization and death from COVID-19, and that the priority is getting first shots to the unvaccinated. But there’s a growing push to shore up protection against “breakthrough” infections and the extra-contagious delta variant of the coronavirus.

Booster doses of Pfizer’s vaccine began last month for people at high risk of COVID-19, and the FDA advisory panel has recommended the same approach for Moderna recipients.

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