(A54) The effect of sex on the incidence, latency, duration and burden of adverse events following influenza vaccination

Publication Number: 337

Background: The annual reformulation of viral strains of the seasonal influenza vaccine results in fluctuating frequencies and severity of adverse effects following immunization (AEFIs), which stresses the importance of pharmacovigilance. Also, sex related factors are known to influence the development of AEFIs.

Objectives: This study aims to describe the difference in incidence and course (i.e. latency time, duration and burden) of AEFIs between males and females after influenza vaccination in the Netherlands.

Methods: We assessed data from a cohort event monitoring study which was repeated for nine consecutive years (2013-2021), each covering several months during the seasonal influenza campaign in the Netherlands. Participants reported demographic information as well as details about AEFIs over a 30-day period in three questionnaires. Logistic regression was used to assess the associations between sex, age, body mass index, study year as a proxy for the vaccines used and comorbidities and the occurrence of any AEFI, local reactions, fever and the five most reported AEFIs (headache, myalgia, fatigue, malaise and nasopharyngitis) by calculating odds ratios (ORs) with their corresponding 95% confidence interval (CI). The difference in latency time, duration and burden between males and females was analyzed by the Kruskal-Wallis test.

Results: The cohort included 7,789 participants (53.0% females), of which 2,691 reported at least one AEFI (68.9% females). The odds of developing any AEFI was 2.58-fold (95%CI 2.31-2.87) higher in females compared to males. Also for fever, local reactions, headache, myalgia and fatigue the odds were significantly higher in females, with ORs ranging from 1.39 to 3.85. Some study years and comorbidities were significantly positively associated with AEFI incidence, whereas age was negatively associated. An AEFI had a significant shorter latency time, a longer duration and a higher perceived burden in females compared to males.

Conclusions: Overall, our results confirm that females experience AEFIs more often than males while the course of AEFIs only partially differs between the sexes. These findings aid in the gain of knowledge regarding differences in response to vaccination between males and females and might contribute to providing more targeted information to people eligible for influenza vaccination about what to expected after vaccination regarding AEFIs.