People “up to date” with their COVID-19 vaccinations are more likely to get infected, according to a new study.
Vaccinated people who received one of the updated bivalent vaccines had a higher risk of becoming infected when compared to people who had not—a group that included both vaccinated and unvaccinated people—researchers with the Cleveland Clinic in Ohio found.
The higher risk held even after adjusting for factors such as age and job location.
“This study highlights the challenges of counting on protection from a vaccine when the effectiveness of the vaccine decreases over time as new variants emerge that are antigenically very different from those used to develop the vaccine,” Dr. Nabin Shrestha and other researchers said.
The Omicron XBB subvariant became dominant in the United States in January. The bivalent vaccines from Moderna and Pfizer target BA.4 and BA.5, in addition to the old Wuhan strain.
The study, published on the medRxiv server (pdf) on June 12 ahead of peer review, included 48,344 employees of the Cleveland Clinic, 47 percent of whom had evidence of prior infection. Employees were included if they were employed in the fall of 2022, when the bivalent vaccines first became available, and were still employed when the XBB strain and its lineages became dominant. The study covered Jan. 29, 2023, to May 10, 2023. People whose age and sex weren’t available were excluded.
Analyzing the vaccine effectiveness with a Simon-Makuch hazard plot, the researchers treated each employee as “not up to date.” When a worker received a bivalent dose, they started counting as “up to date.” Employees stopped being counted if they were fired.
During the study period, 1,475, or 3 percent of clinic employees, became infected.
Being “not up to date” was associated with a lower risk of infection, with an unadjusted hazard ratio of 0.78 and an adjusted hazard ratio of 0.77. A hazard ratio under one means a smaller risk of infection.
Researchers did not provide vaccine effectiveness estimates because they did not calculate how many of the infected employees were unvaccinated, Shrestha told The Epoch Times via email. Most employees, 87 percent, had received at least one dose of a vaccine.
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