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.
That’s the takeaway from a study released Tuesday morning from the Centers for Disease Control and Prevention, which offered the first clinical efficacy data for the bivalent shot since its national rollout in September.
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.
The real-world look at the relative efficacy was based on data from 360,000 people. CDC researchers conducted the study between September 14 and October 11, when the omicron subvariants BA.4/5 and their sublineages dominated.
The study enrolled people already tapped into a national program aimed at increasing COVID-19 testing in areas with high social vulnerability. The study looked at people with COVID-19-like symptoms who came into partnering retail pharmacies for COVID-19 testing. Researchers collected their test results as well as their vaccination and infection history and other medical information. The study excluded people who were immunocompromised.
Of the 360,626 tests given, 121,687 (34 percent) were positive for COVID-19. 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.
Relative effectiveness
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. And in those age 65 or older, rVE ranged from 28 percent to 43 percent.
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