The U.S. Food and Drug Administration (FDA) on Tuesday authorized a fourth dose of Pfizer-BioNTech’s or Moderna’s anti-covid vaccines for people over 50, as authorities warn of a possible new wave of the pandemic.
The FDA said in a statement that it based its decision on emerging evidence that an additional booster dose, applied four months after the last one, improved protection against severe COVID and was not associated with new safety concerns.
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In addition, immunocompromised people who have already received four injections, with the last one at least four months ago, are now eligible for a fifth dose. Among these people are those who received organ transplants.
Pfizer’s vaccine will be available to immunocompromised people over the age of 12, while the Moderna vaccine will be available to those 18 and older.
“Current evidence suggests some decreased protection over time against severe COVID-19 outcomes in older, immunocompromised people,” said FDA senior scientist Peter Marks in explaining the decision.
The FDA said data from Israel, where the effects of a fourth dose given four months after the third on 700,000 people were studied, found an additional injection to be safe.
He also cited data from a study of 154 healthcare workers whose antibody levels, including against the delta and omicron variants, rose two weeks after receiving the fourth dose.
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A study published by Israeli researchers in the New England Journal of Medicine this month indicated that three doses of messenger RNA vaccines of the current generation had peaked in terms of the immune response generated.
In other words, while three doses increase immunity levels, the fourth dose restores antibody levels to where they were shortly after the third.
Experts noted that the benefits for younger, healthier people are still unclear, and say new vaccines will likely need to be developed as the virus continues to mutate seasonally.
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