In a report published in the Morbidity and Mortality Weekly Report, scientists at the U.S. Centers for Disease Control and Prevention (CDC) provided the first real-world evidence on the effectiveness of the bivalent booster shot that the CDC and the U.S. Food and Drug Administration (FDA) authorized in September.
The researchers conclude that the bivalent booster, which contains genetic material from both the original SARS-CoV-2 virus and the Omicron BA.4/5 variants, is effective in protecting people from severe COVID-19. The relative effectiveness among people ages 18 to 49 who received the bivalent booster—compared to those who received more than two shots of the original vaccine—ranged from 30% if their last original vaccine dose was two to three months earlier, to 56% if their last original vaccine dose was more than eight months prior to the new one. The effectiveness was slightly lower for older people, ranging from 28% to 48% among those 50 years and older.
The fact that the vaccine effectiveness increased with more time since the last original vaccine dose shows that the new booster replenishes waning levels of virus-fighting antibodies, the researchers write.
The data came from the national Increasing Community Access to Testing program, which provides free COVID-19 tests at pharmacies around the country. Between Sept. 14 and Nov. 11, more than 360,000 tests for SARS-CoV-2 were performed at nearly 1,000 sites, and people were asked to report their vaccination status and previous infection history. During that time, Omicron variants BA.4/5 were dominant, but newer variants, including BQ.1 and BQ.1.1, which now account for nearly 50% of cases in the U.S., were beginning to increase. The researchers say that the data during periods when just BA.4/5 dominated were not significantly different with respect to the Omicron booster’s effectiveness when compared to periods when other variants emerged. Still, the researchers acknowledge that the results may change as newer variants take over.
Other researchers are investigating how the updated bivalent booster affects immunity—not just to the variants it targets, but also to previous and even potentially newer variants that evolve from BA.4/5. Some data suggest that vaccine-induced immunity might provide higher levels of virus-neutralizing antibodies than getting infected with the virus might, possibly because the immune system sees and reacts to vaccines in a different way than it sees and responds to pathogens like viruses. And each vaccination may also help the immune system to become more efficient at recognizing and disabling the virus.
The current real-world findings, the study authors say, point to the need to stay up to date with COVID-19 vaccines, including getting the latest Omicron booster. 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,” the study authors write.