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October 13, 2022 11:41 AM EDT

Pfizer-BioNTech announced that they now have the first human data hinting at how effective the new Omicron booster might be. The updated bivalent vaccine targets both the original SARS-CoV-2 strain and the currently circulating Omicron BA.4/5 variants and is authorized for use in Americans age 12 and older (and soon for ages 5 and older in a kid-sized 10 mcg dose, pending sign-off from the U.S. Centers for Disease Control and Prevention). That authorization was granted based on safety and efficacy studies in animals and data from a different vaccine targeting BA.1.

In the first results from human studies—which were announced by press release on Oct. 13 and not yet published in full—Pfizer-BioNTech reports that 40 people ages 18 to 55 who were boosted with the bivalent shot produced higher levels of virus-fighting antibodies against Omicron BA.4/5 seven days later compared to their starting levels. Among people 55 and older, those who received the Omicron booster generated higher levels of Omicron antibodies compared to those boosted with the original vaccine. That people produced more Omicron-specific antibodies after the booster is encouraging, especially since people in the study hadn’t been boosted for 11 months, on average, before receiving the bivalent vaccine. The companies did not provide a more detailed breakdown of the difference in the levels in their press release, but more data are expected in a few weeks.

The results are the first from an ongoing study involving more than 900 people 12 years and older who are receiving the Omicron booster at one of two doses: 30 mcg or 60 mcg. Everyone in the study has been boosted at least once with the original vaccine (which means they received at least three doses of the original shot). Their immune responses will be compared to those from people who have previously received two booster shots, or four doses, of the original vaccine. The FDA authorized the booster at the 30 mcg dose, but the trial will investigate whether the higher dose would provide additional protection. The companies plan to continue studying the Omicron BA.4/5 bivalent booster in younger children as well.

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