2 enhanced flu vaccines offer similar protection against infection in older adults
Laine BergesonToday at 9:39 a.m.
Influenza, General
Influenza Vaccines
Adjuvanted and high-dose influenza vaccines showed comparable effectiveness against test-confirmed flu and hospitalization in older adults in all studied settings, according to a new study published in the International Journal of Infectious Diseases.
Both vaccines are designed to improve immune responses in adults aged 65 and older, who are at higher risk of severe outcomes and have attenuated immune responses to vaccination. Adjuvanted vaccines contain an ingredient that helps boost the body’s immune response, while high-dose vaccines contain more of the viral antigen.
For the study, researchers led by a team at flu vaccine maker CSL Seqirus in Quebec, Canada, analyzed data from US adults aged 65 and older who had been vaccinated with either adjuvanted or high-dose flu vaccines during the 2023–24 respiratory virus season.
The adults all sought care for acute respiratory illness or an illness involving fever and were tested for flu. Of the 37,377 people included in the analysis, 3,174 (8.5%) tested positive for flu.
Findings align with previous research
The researchers found no statistically significant difference in effectiveness between receipt of the adjuvanted and high-dose vaccines.The estimated relative effectiveness of the adjuvanted flu vaccine compared with the high-dose flu vaccine was –0.9% across all settings and 0.5% in emergency departments and hospitals. Pooled analyses estimated a relative vaccine effectiveness against hospitalization from 2022 to 2024 of −0.5% overall and −1.3% in the high-risk subgroup. The confidence intervals were fairly wide, though, indicating imprecision.
The study compared the two vaccines to each other but did not estimate their protection relative to remaining unvaccinated.
The findings were consistent with previous research, including an analysis of the 2022–23 flu season, which found comparable effectiveness between adjuvanted and high-dose flu vaccines.
Note the researchers, “This is further supported by a systematic review and meta-analysis of 10 studies reporting comparable effectiveness of both vaccine types across clinical endpoints, as well as evidence showing improved protection of both vaccines compared with standard-dose influenza vaccines in adults ≥65 years.”
CSL Seqirus, which manufactures Fluad, an adjuvanted trivalent/quadrivalent influenza vaccine, funded the study and contributed to its design, interpretation, and writing.