The updated COVID-19 vaccines administered this fall and winter were found to be 54 percent effective at preventing symptomatic infections among adults, according to an early analysis released by the Centers for Disease Control and Prevention (CDC), with researchers finding that the shot was protective against the dominant JN.1 subvariant.
Through the CDC’s Increasing Community Access to Testing program that provides free testing to uninsured individuals, researchers gathered data on patients who experienced COVID-19-like symptoms.
The data was sourced from tests conducted at participating CVS Pharmacy and Walgreens locations from September 2023 to January 2024.
Using patients who tested negative for COVID-19 as a control group, researchers compared the rate of self-reported symptoms occurring as well as history of infection and immunization between the control and those who tested positive.
Among the 9,222 tests that were deemed eligible for analysis, vaccine effectiveness was found to be 54 percent among adults over the age of 18.
“Updated monovalent COVID-19 vaccines provided 54% (95% CI = 46–60%) protection against symptomatic SARS-CoV-2 infection in persons recently vaccinated compared with those who did not receive an updated vaccine dose,” according to the analysis. “Vaccination provided protection for infections caused by JN.1 and infections caused by XBB-related lineages.”
Though the updated vaccines from Pfizer, Moderna and Novavax were designed to protect against the XBB.1.5 omicron subvariant, health officials anticipated and hoped that dominant strains that arose by the time doses were administered would be closely related enough for the shots to still be effective.
According to the most recent federal surveillance data, the JN.1 omicron subvariant currently accounts for about 86 percent of COVID-19 infections in the U.S.
The report acknowledged some limitations within this analysis. As patient history of immunization, underlying medical conditions and infection was self-reported, these results could be subject to recall bias. It was also noted that these results were derived from a population of people who chose to get tested for SARS-CoV-2, meaning there could be additional biases affecting the data.
