Department of Research & Evaluation News

High-dose and adjuvanted influenza (flu) vaccines boosted protection against flu symptoms and hospitalization for people 65 years and older during the 2022-2023 flu season compared to the standard flu vaccine. The study was published on August 21, 2024, in Clinical Infectious Diseases.

“Our research showed that there were advantages for older people to receive high-dose or adjuvanted flu vaccines over the standard vaccine,” said Jennifer Ku, PhD, MPH, an infectious disease epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation. “While seasonal variation exists, it is expected that seniors will continue to benefit from flu vaccines that are stronger than the traditional standard-dose vaccines.”

Vaccination is the best way to prevent flu and reduce the severity of flu symptoms. Typically, flu vaccines are made by incubating the viruses in chicken eggs. To improve flu vaccine performance and its production, high-dose, adjuvanted, and recombinant vaccines became available. High-dose vaccine is four times higher-dose than regular flu vaccines, while adjuvanted vaccines have an additional ingredient to boost the immune system. Recombinant vaccines are produced using recombinant technology that does not rely on eggs in the manufacturing process. They were not widely administered within Kaiser Permanente in Southern California and so were not included in this study.

In 2022, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices made a recommendation to use high-dose, adjuvanted, or recombinant vaccines over standard dose vaccines for adults aged 65 years and older. Individuals in this age group are at increased risk for severe illness, hospitalization, and death due to flu.

This Kaiser Permanente real-world study was the first to compare the high-dose and adjuvanted vaccines against the standard vaccines since the recommendation was issued. The study included nearly a half-million people aged 65 years and older who received one or more doses of flu vaccine during the 2022-2023 flu season.

• As compared to standard dose flu vaccine, the vaccine effectiveness of high-dose and adjuvanted flu vaccine against hospitalization for flu was estimated as 25% and 62%, respectively.
• As compared to standard dose flu vaccine, the vaccine effectiveness of high-dose and adjuvanted flu vaccine against health care visits for flu was estimated at 9% and 17%, respectively.

“Previous studies had compared people who were vaccinated against flu to those who weren’t. This was the first real-world study to compare high-dose and adjuvanted flu vaccines to the more traditional standard-dose egg-based vaccines after the preferential recommendation was made by ACIP. We found that high-dose and adjuvanted flu vaccines offered additional protection against flu-related visits and hospitalizations as compared to standard flu vaccines in older adults,” said the senior author on the paper, Hung Fu Tseng, PhD, MPH, a senior scientist with the Department of Research & Evaluation. “Our study findings support ACIP’s recommendation to vaccinate seniors with high-dose and adjuvanted flu vaccines.”

Additional authors on the study include co-first author Emily Rayens, PhD, MPH; Lina S. Sy, MPH; Lei Qian, PhD; Bradley K. Ackerson, MD; Yi Luo, PhD; Julia E. Tubert, MPH; Gina S. Lee, MPH; Punam P. Modha, MPH, of the Department of Research & Evaluation; and Yoonyoung Park, ScD; Tianyu Sun, PhD; Evan J. Anderson, MD, of Moderna.