The panel approved booster doses of the Pfizer vaccine, developed with BioNTech SE, for all adults at least six months after their second vaccine. For the immunocompromised, extra doses of either shot may be given at least 28 days after the second one, it said on Monday.

“Studies showed that an extra dose of these vaccines increased the ability to produce antibodies against the virus that causes COVID-19 in organ transplant patients with weakened immune systems,” the European Medicines Agency said in a statement. “It is expected that the extra dose would increase protection at least in some patients.”

The EMA committee is following the U.S. and other countries with ample vaccine supplies in allocating doses or considering the move for booster shots. The U.S. Food and Drug Administration may soon authorize half-dose boosters of the Moderna vaccine, setting the stage to further widen the U.S. booster campaign after earlier authorization of the extra Pfizer-BioNTech dose. 

Concern about withering COVID protection prompted Israel—one of the first countries to start vaccinating its population—to begin administering booster shots months ago. 

Some experts have questioned the need for the broad use of boosters, while the World Health Organization has called for a moratorium on them this year, until more people outside of rich countries get protection. An all-star panel of scientists weighed in last month, saying the initial shots work so well that most people don’t yet require a third injection.

Governments would be better served to focus on immunizing the unvaccinated and to wait for more data on which boosters would be most effective and at what doses, the authors, who included two prominent FDA experts, argued in the medical journal The Lancet. They based their assessment on a wide range of real-world observational studies as well as data from clinical trials.

In the EU, public health bodies at the national level may issue official recommendations on the use of booster doses, “taking into account emerging effectiveness data and the limited safety data,” the EMA said in the statement. 

“The risk of inflammatory heart conditions or other very rare side effects after a booster is not known and is being carefully monitored,” it said. 

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