There hasn’t been enough research on how much protection a fourth dose can offer, medical professionals told CNBC.
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The Food and Drug Administration on Thursday said vaccine manufacturers should update their Covid-19 booster shots to target the most recent omicron subvariants that are gaining ground in the U.S.
Dr. Peter Marks, head of the FDA’s vaccine division, said manufacturers should update their shots to target omicron BA.4 and BA.5 in addition to the original strain of the virus that first emerged in Wuhan, China in 2019.
The FDA’s panel of independent experts voted overwhelmingly on Tuesday to recommend a vaccine switch after an all-day meeting in which they evaluated the benefits and downsides of updating the shots.
The vaccine makers are having trouble keeping up with the rapid evolution of the virus. Pfizer and Moderna developed their omicron shots to target the original version of the variant, BA.1., which caused the massive wave of infection over the winter.
However, BA.1 has been pushed out by other omicron subvariants and is no longer circulating in the U.S. Omicron BA.4 and BA.5 now make up more than 50% of Covid infections in the U.S., according to the Centers for Disease Control and Prevention.
Pfizer and Moderna presented clinical trial data on Tuesday demonstrating that their updated shots triggered a stronger immune response against omicron BA.1 than the original version of the vaccines based only on the strain that emerged in Wuhan. The updated shots, based on BA.1, did not perform as well against BA.4 and BA.5, though the immune response was still robust.
However, the studies were small with only a few hundreds participants, and there’s currently no data on how well the shots will perform in the real world. The immune response is generally viewed as a good indicator of how well the vaccines will protect against illness.
It’s unclear how long it will take for the vaccine makers to switch gears and develop shots that include BA.4 and BA.5. Marks said said the FDA has asked the companies to start clinical trials on these newer subvariants.
The two dose primary vaccination series will not change for now, Marks said. The FDA wants to update the booster shots to provide more durable protection ahead of the fall, when public health experts expect another wave of infection as immunity from the vaccines wanes and people head indoors to escape the weather. Covid spreads more easily indoors.
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