WASHINGTON >> Although new federal data suggests that the effectiveness of booster shots wanes after about four months, the Biden administration is not planning to recommend fourth doses of the coronavirus vaccine anytime soon.

“We simply don’t have enough data to know that it’s a good thing to do,” Dr. Peter Marks, who heads the division of the Food and Drug Administration that regulates vaccines, said this week.

Dr. Anthony Fauci, chief medical adviser to the White House, said the vaccines are still a firm bulwark against severe illness, despite data from the Centers for Disease Control and Prevention showing that booster shots lose some of their potency after four to five months.

The CDC’s research, released last Friday, analyzed hospitalizations and visits to emergency rooms and urgent care clinics in 10 states by people who had had booster shots of either Moderna’s or Pfizer’s vaccine. The study showed the level of protection against hospitalization fell from 91% in the two months after a third shot to 78% after four to five months. Effectiveness against visits to emergency rooms or urgent care clinics declined from 87% to 66%.

The data came with major caveats: Researchers did not examine variations by age group, underlying medical conditions or the presence of immune deficiencies. Still, they said, the findings underscored the possible importance of a fourth shot.

“‘Should I get a fourth shot?’ That’s what a lot of people are asking me,” Fauci said. “The answer is if you look at where we are now, it looks like it’s good protection. Seventy-eight percent is good.”

The administration’s vaccine strategy has been under constant review since President Joe Biden took office. What comes next, Fauci said, will depend on whether protection from boosters holds steady or continues to drop after four to five months.

Marks said it may turn out that the best time for an additional shot is this fall, when the spread of the coronavirus is expected to pick up again. “Barring any surprises from new variants, maybe the best thing is to think about our booster strategy in conjunction with the influenza vaccine next fall and get as many people as possible boosted then,” he said.

This article originally appeared in The New York Times.

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