(361) Sex Inequity in Access to Safe Vaccination: A Sex Disaggregated Comparative Analysis of Vaccine Safety Surveillance Reports and Social Media Vaccine-Related Health Mentions.

Background: Immunisation is a public health wonder of modern science, but all is not fair between the sexes. Clinical trials frequently aggregate safety results across all sexes and adverse events (AE) following immunisation in post-licensure surveillance appear under-reported in men.

Objectives: To compare vaccine-associated AE between males and females in spontaneous reports and social media mentions.

Methods: We reviewed 45,018 COVID-19 AE reports to the vaccine safety surveillance system of Victoria, Australia (SAEFVIC) by 20 May 2023, and considered sex-specific imbalances. Reporting rate (RR) per 100,000 doses administered and female to male reporting rate ratios (RRR), stratified by 10-year age-groups were calculated.
We interrogated social media (X, formerly Twitter) using previously validated machine-learning topic modelling to identify sex-identifiable personal vaccine-associated health mentions and compared with spontaneous reported AE reactions.

Results: Post-licensure surveillance reporting was almost twice as high for females than males (RRR 1.8 1, 95%CI 1.77, 1.84). This association varied by age, being not evident below 18-years of age (RRR 1.10), peaking at RRR 2.15 (95%CI 2.05, 2.24) at 40–49 years, and diminishing after 60 years of age (RRR 1.34).
Reproductive health related reactions that would differ by sex did not account for this difference, as just 1.44% of adults (526/36,456 ) reported these reactions.

While expected sex-aligned signals of female vulval ulcers and male myo-pericarditis predominance were evident, many other AE had significant sex-imbalanced reporting rates. For reactions with count >10, 81 had >3.0 RRR for females and just 8 RRR < 0.7 for males: only some with plausible clinical explanation. Overall, the proportion of adult males self-reporting (10.9%) was two-thirds that of females (p < 0.0001) but conversely 25% more likely to be serious AE (20.2%, p< 0.0001), suggesting spontaneous surveillance captures only the tip of the iceberg of males' experience. This finding was affirmed as analysis of social media personal health mentions identified several new male vaccine-associated AE concerns, notably swollen testicles, persistent erections and prostate cancer.

Conclusions: We identified sex disproportionality in vaccine pharmacovigilance. Females experience a wider range of AE than males, however males appear to be under-reporting, suggesting traditional surveillance has reduced ability to detect safety signals or address concerns of male adults. This underlines the importance of adjunctive surveillance methodologies including social media and large database analyses to ameliorate this risk, validate community experiences and create opportunities to redress inequity in access to safe vaccination.