Before that, debate continued on whether the more powerful vaccines actually made a difference.
Now, a new study has found that during the 2022–2023 flu season, the enhanced flu shots appeared to offer greater protection compared with the standard flu vaccine. The results were published in Clinical Infectious Diseases.
“Our research showed that there were advantages for older people to receive high-dose (HD) or adjuvanted flu vaccines over the standard vaccine,” said Jennifer Ku, PhD, MPH, an infectious disease epidemiologist with the Kaiser Permanente Southern California (KPSD) Department of Research and 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.”
The study pointed out that influenza causes substantial morbidity, especially among older adults, and that updated data on the effectiveness of currently licensed vaccines was lacking for this population.
The cohort study conducted at KPSD evaluated comparative vaccine effectiveness (cVE) of HD, adjuvanted, and standard-dose (SD) cell-based influenza vaccines compared with the SD egg-based vaccine. The participants were 495,119 adults aged 65 years and older who received an influenza vaccine between August 1, 2022, and December 31, 2022, with a follow-up to May 20, 2023. Most (54.9%) were female, 46.3% were non-Hispanic white, and the median age was 73 years.
The primary outcomes were defined as influenza-related medical encounters and polymerase chain reaction (PCR)–confirmed influenza-related hospitalization.
The results indicated that adjusted cVEs against influenza-related medical encounters in the HD, adjuvanted, and SD cell-based vaccine groups were 9.1% (95% CI; 0.9, 16.7), 16.9% (95% CI; 1.7, 29.8), and –6.3 (95% CI; –18.3, 6.9), respectively. At the same time, adjusted cVEs against PCR-confirmed hospitalization in the HD, adjuvanted, and SD cell-based groups were 25.1% (95% CI; 0.2, 43.8), 61.6% (95% CI; 18.1, 82.0), and 26.4% (95% CI; –18.3, 55.7), respectively.
“Compared to the SD egg-based vaccine, HD and adjuvanted vaccines conferred additional protection against influenza-related outcomes in the 2022-2023 season in adults ≥65 years,” the study team reported. “Our results provide real-world evidence of the comparative effectiveness of currently licensed vaccines.”
Background information in the article advises that the HD vaccine is four times higher dose than regular flu vaccines, while adjuvanted vaccines have an additional ingredient to boost the immune system.
In 2022, the CDC’s Advisory Committee on Immunization Practices (ACIP) first made a recommendation to use HD, adjuvanted, or recombinant vaccines over SD vaccines for adults aged 65 years and older. The reason is that people in that age group are at increased risk for severe illness, hospitalization, and death due to flu.
“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,” said senior author Hung Fu Tseng, PhD, MPH, a senior scientist with the KPSD Department of Research and Evaluation. “Our study findings support ACIP’s recommendation to vaccinate seniors with high-dose and adjuvanted flu vaccines.”
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