Adjuvanted influenza vaccines and high-dose influenza vaccines may have similar effectiveness in adult patients

1. Adjuvanted influenza vaccines did not differ significantly in effectiveness compared to high-dose influenza vaccines against laboratory-confirmed influenza and influenza-related hospitalizations or emergency department (ED) visits in adult patients.

Evidence Rating Level: 1 (Excellent)

Influenza burden is greatest among older adults, with 70% to 85% of influenza-related deaths and 50% to 70% of influenza-related hospitalizations occurring among adults aged 65 years or older. Current guidelines recommend either an adjuvanted inactivated influenza vaccine or a high-dose influenza vaccine, both of which have been shown to provide greater protection compared to standard-dose influenza vaccines. However, no randomized studies have compared the effectiveness of adjuvanted and high-dose vaccines. This cluster-randomized crossover study included patients aged 65 years or older across 65 healthcare facilities within a healthcare system. These facilities were randomized to block A (33 facilities) or block B (32 facilities). In the first week of the influenza vaccination season, block A facilities administered high-dose vaccines and block B facilities administered adjuvanted vaccines. Each facility switched to the other formulation for every week thereafter. Of 429,595 patients, 212,875 (49.6%; mean [SD] age, 75 [7] years; 55.1% female) received adjuvanted vaccine, and 216,720 (50.4%; mean [SD] age, 75 [7] years; 55.2% female) received high-dose influenza vaccine. The primary outcome was PCR-confirmed influenza in any clinical setting. Among those receiving an adjuvanted influenza vaccine, 22,650 had a polymerase chain reaction (PCR) test (10.6%), and 836 tested positive for influenza (3.93 per 1000 persons), of whom 411 (49.2%) were hospitalized (n = 169) or had an ED visit (n = 242) for influenza (1.93 per 1000 persons). Among those receiving a high-dose influenza vaccine, 22,887 had a PCR test (10.6%), and 867 tested positive for influenza (4.00 per 1000 persons), of whom 466 (53.7%) were hospitalized (n = 196) or had an ED visit (n = 270) for influenza (2.15 per 1000 persons). The relative vaccine effectiveness of adjuvanted compared with high-dose influenza vaccine was 1.5% (95% CI, −8.4% to 10.5%) against influenza and 9.1% (95% CI, −4.0% to 20.4%) against influenza with hospitalization or emergency department visits. Therefore, there is no significant difference in effectiveness between adjuvanted and high-dose influenza vaccines, supporting current guidelines recommending either one in adults 65 years or older.

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