Department of Research & Evaluation News

Emerging COVID-19 variants continue to cause serious COVID-19 disease, but most people have not received any COVID-19 vaccine for more than a year. Kaiser Permanente Southern California researchers assessed the effectiveness of bivalent COVID-19 vaccines against the recently circulating variants or sublineages to inform policymakers and the potential need for updated vaccines.

One of the latest studies found that the Moderna BA.4/BA.5 bivalent vaccine effectiveness against infection, emergency department and urgent care visits, and hospitalization with BA.4/BA.5-related and XBB-related sublineages waned over time and differed by infecting variant. The team concluded that periodic vaccination with vaccines reflecting the current circulating variants reduces SARS-CoV-2–associated illness and hospitalization.

This was the first study to assess Moderna bivalent vaccine effectiveness against severe outcomes with sequencing-confirmed XBB-related sublineages.

Bradley Ackerson, MD, a Kaiser Permanente South Bay Medical Center pediatric infectious disease specialist and a researcher, presented the study findings to the World Health Organization Vaccine Effectiveness forum on March 5, 2024. The study was published in Human Vaccines and Immunotherapeutics on April 4, 2024.

“Moderna bivalent vaccine effectiveness waned over time with little protection against emergency department and urgent care visits with COVID-19 about 4 months after vaccination. Moderna bivalent vaccination provided only modest protection against hospitalization for COVID-19 about 6 months after vaccination,” Dr. Ackerson said. “Therefore, our findings underscore the importance of receiving COVID-19 vaccinations as recommended in order to avoid COVID-19 disease that remains even more common and more serious than influenza-associated disease.”

The study was conducted at Kaiser Permanente Southern California. It included subgroup analyses by age group (≤17, 18–64, and ≥65 years), among people who were immunocompromised, and among people with a known history of COVID-19 infection. A total of 83,864 members were included in this study.

The study found that Moderna bivalent vaccine effectiveness against infection and emergency department encounters with BA.4/BA.5 or XBB was initially similar, but protection against infection with XBB waned and was minimal after 120 days. Although Moderna bivalent vaccine effectiveness against hospitalization for BA.4/BA.5 or XBB was high initially and waned more slowly than vaccine effectiveness against infection and emergency department and urgent care visits, effectiveness against hospitalization for XBB declined to 30% after more than 180 days.

“These results highlight the need for periodic COVID-19 vaccination as protection wanes against infection and hospitalization, even when the vaccine is well matched to circulating variants,” said the research senior author, Hung Fu Tseng, PhD, MPH, a scientist with the Kaiser Permanente Southern California Department of Research & Evaluation. “Furthermore, these findings suggest that periodic adjustment of vaccines to better target emerging variants that can escape vaccine and infection-induced immunity may be beneficial.”

The research was funded by Moderna Inc.

In addition to Dr. Ackerson and Dr. Tseng, Kaiser Permanente co-authors on the research included Katia J. Bruxvoort, PhD, MPH; Lei Qian, PhD; Lina S. Sy, MPH; Sijia Qiu, MS; Julia E. Tubert, MPH; Gina S. Lee, MPH; Jennifer H. Ku, PhD, MPH; Ana Florea, PhD, MPH; Yi Luo, PhD; Radha Bathala, MS; Julie Stern, MPH; Soon K. Choi, MPP; MSc, Harpreet S. Takhar, MPH; and Michael Aragones, MD.