First efficacy data on bivalent boosters shows they work against infection

The updated bivalent COVID-19 booster vaccine increased protection against symptomatic disease compared with the original monovalent vaccine given as recently as two months ago.

In adults, the relative effectiveness of the bivalent vaccine's protection against symptomatic infection ranged from about 30 percent to up to 56 percent compared with that of the monovalent vaccine, with the relative efficacy estimated to be larger the more time had passed since a person's last monovalent shot.

Of just the positive tests, 28,874 (24 percent) were among unvaccinated people, 87,013 (72 percent) were from people who had received between two and four monovalent vaccine doses but no bivalent booster dose, and 5,800 (5 percent) had received a bivalent booster dose.

For people ages 18 to 49, the relative vaccine effectiveness (rVE) for a bivalent booster against a symptomatic infection was 30 percent compared with people who had received two or more monovalent doses, with their most recent shot between two to three months ago.

The rVE in this age group jumped to 56 percent when compared to people with two more monovalent doses, if the most recent dose was given eight or more months ago.

For the same comparisons in people ages 50 to 64, rVE ranged from 31 percent to 48 percent.

"Results from this study show that bivalent boosters provide protection against symptomatic SARS-CoV-2 infection during circulation of BA.4/BA.5 and their sublineages and restore protection observed to wane after monovalent vaccine receipt, as demonstrated by increased rVE with longer time since the most recent monovalent dose," the CDC authors concluded.

"All persons should stay up to date with recommended COVID-19 vaccines, including bivalent booster doses, if it has been ≥2 months since their last monovalent vaccine dose.".

Currently, only 11.3 percent of eligible Americans have received a bivalent booster shot.