Enhanced passive safety surveillance of standard-dose and high-dose influenza vaccines in Finland and Germany 2023–24 season

Abstract

Enhanced Passive Safety Surveillance was used to detect safety signals before the peak period of immunization with quadrivalent inactivated influenza vaccines (IIV4) in Finland (standard dose [SD]) and Germany (high dose [HD]) in the 2023–24 season. The primary objective was to evaluate adverse drug reactions (ADRs) occurring ≤7 days following IIV4 vaccination. Enrolled participants were vaccinated in routine clinical care settings and encouraged to report ADRs. Exposure data and ADR reports were collected in a near real-time manner using an electronic system. Vaccinee reporting rate (RR) with 95% confidence interval (CI) was calculated as the number of vaccinees reporting ≥ 1 ADR divided by total number of vaccinees. In Finland for SD-IIV4, among 1,003 vaccinees aged ≥ 6 months, 81 reported a total of 192 suspected ADRs occurring ≤ 7 days following vaccination (vaccinee RR 8.08%; 95% CI 6.46, 9.94). In Germany for HD-IIV4, among 1,075 vaccinees aged ≥ 60 years, 15 reported 46 ADRs that occurred in ≤ 7 days of vaccination (vaccinee RR 1.40%; 95% CI 0.78, 2.29). No safety signal was detected during this surveillance. The 2023–24 season surveillance did not suggest any clinically significant changes in safety profile compared with previously reported safety data for SD-IIV4 and HD-IIV4.