The agency that regulates the drug and food industry in the United States (FDA, its acronym in English) authorized, this Tuesday (29), a fourth dose of Pfizer/BioNTech or Moderna Covid vaccines for people over 50 years. The approval comes at a time when authorities are warning of a possible new wave of the pandemic.
In a statement, the FDA said it based its decision on emerging evidence that an additional booster dose, given four months after the last one, improved protection against severe Covid-19 and was not associated with new safety issues.
In addition, immunocompromised people who have already received four injections, the last one being at least four months ago, are now eligible for a fifth dose. This group includes those who have received organ transplants.
Pfizer’s vaccine will be available to immunocompromised people over the age of 12, and Moderna’s will be available to people over 18.
“Current evidence suggests some waning protection over time against severe Covid-19 outcomes in the elderly and immunocompromised,” said FDA lead 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 in 700,000 people were studied, showed that an additional injection was safe.
The agency also cited data from a study of 154 healthcare workers whose antibody levels, including those against the delta and omicron variants, rose two weeks after receiving the fourth dose.
A study published by Israeli researchers in the New England Journal of Medicine this month showed that three doses of current-generation messenger RNA vaccines peaked in terms of the immune response generated.
In other words, while three doses boost immunity levels, the fourth dose restores antibody levels to where they were right after the third.
Experts note that the benefits for younger, healthier people are still unclear and say new vaccines are likely to be developed as the virus continues to mutate seasonally.
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