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The bivalent COVID-19 booster that received emergency use authorization from the U.S. FDA at the end of August comes to the market without much specific data behind it (NEJM JW Gen Med Oct 1 2022). Instead, regulators relied heavily on studies of analogous bivalent boosters directed at earlier circulating Omicron strains.
One such study is an ongoing multicenter industry-supported trial that enrolled about 800 vaccinated and boosted U.S. adults in the spring of 2022. Researchers provided a second booster, consisting of either mRNA directed exclusively against the ancestral SARS-CoV-2 strain circulating in the spring of 2020 or mRNA directed against both the ancestral strain and an early Omicron variant (BA.1).
After 4 weeks, titers of neutral…