PHILADELPHIA, PA—High-dose—versus standard-dose—inactivated influenza vaccine resulted in a significantly shorter duration of laboratory-confirmed influenza respiratory illness in older adults, according to results of a multicenter study reported at IDWeek 2014.

Fewer symptoms were also reported, noted H. Keipp Talbot, MD, MPH, of Vanderbilt University School of Medicine in Nashville, TN, and colleagues. They also found that rates of cardio-respiratory events and hospitalizations within 30 days of laboratory-confirmed influenza were lower after high-dose vaccination; however, there were too few comparative cases to reach statistical significance.

Previous research has shown that the high-dose inactivated influenza vaccine induces higher antibody responses and provides improved protection against illness from influenza. In this randomized, double-blind, active-controlled study, the investigators evaluated the vaccine’s effect on disease modulation.

The study randomly assigned 31,989 adults ≥65 years of age to high-dose inactivated influenza vaccine (60µg of hemagglutinin [HA] per strain; n=15,991) or standard-dose inactivated influenza vaccine (15µg of HA per strain; n=15,998). Participants were instructed to contact their study site if they experienced a respiratory illness.

At the site, a nasopharyngeal swab was collected within 5 days of onset of the respiratory illness for confirmation of influenza, either by culture or polymerase chain reaction. Data on illness duration and symptoms were collected, as was occurrence of cardio-respiratory events and hospitalizations within 30 days of onset. Three blinded physician reviewers determined whether to attribute cardio-respiratory events and hospitalizations to influenza.

Dr. Talbot reported that a laboratory-confirmed influenza respiratory illness occurred in 316 (1.98%) of the high-dose vaccine recipients and 387 (2.42%) of those who received the low-dose vaccine. Median duration of illness was 11 days (interquartile range [IQR]: 8, 19) for the high-dose vaccine and 14 days (IQR: 8, 21) for the low-dose vaccine (P=0.003).

Participants who received the high-dose inactivated influenza vaccine had fewer symptoms than those in the low-dose group (P=0.04; non-parametric test).

Among those with a laboratory-confirmed influenza respiratory illness, 136 influenza-attributed cardio-respiratory events occurred within 30 days of illness onset, 54 (17.1%) in the high-dose and 82 (21.2%) in the standard-dose vaccine groups (relative risk [RR] 0.81; 95% CI 0.59, 1.10). Of the 10 hospitalizations attributed to influenza that occurred within 30 days of illness onset, 4 (1.27%) were in the high-dose and 6 (1.55%) were in the standard-dose vaccine groups (RR 0.82; 95% CI 0.23, 2.87).

Dr. Talbot concluded that the high-dose vaccine was associated with a shorter duration and fewer influenza respiratory symptoms compared to standard-dose vaccine for lab confirmed influenza.