Women could be more likely to have injection site and systemic reactions to the seasonal flu vaccination than men, Canadian researchers suggests today.
Pooled data analysis of the available evidence, published in the Journal of Epidemiology & Community Health, analyses sex differences that are not usually considered in vaccine programmes/policy.
The researchers, led by Dr Marilou Kiely, from the University of Montreal Department of Microbiology, Infectiology, immunology & Paediatrics, analysed data from 18 comparative clinical trials (phase III) of seasonal flu vaccination, which involved 34,343 adults, and were carried out between 2010 and 2018.
The trial results were pooled and they looked at potential sex differences by age: 18-64 and 65 and over, particularly examining any evidence for injection site and systemic reactions assessed within seven days of vaccination. They also examined specific reactions for each included study, such as pain, redness, fever, headache and myalgia, as well as other health outcomes, assessed three to four weeks afterwards together with any serious outcomes reported during the study period.
There was a 29% increased and 43% increased risk of an injection site reaction in younger and older women, respectively, than it was in men. Women also had a greater risk of systemic reactions than men, regardless of age: 25% higher for younger participants and 27% higher for older participants.
The risk of a severe reaction was twice as high in women as it was in men, and about 50% higher in younger participants for systemic reactions. There were no differences when it came to vaccine type.
The study authors, led by Dr Marilou Kiely, from the University of Montreal, say their results indicate an absolute increase in risk among women of 115 extra cases/1,000 vaccinees of injection site reactions, and 74 extra cases/per 1,000 vaccinees of systemic reactions.
However, they caution, the quality of evidence was low for injection site reactions and moderate for systemic reactions. They add that gender might have influenced outcomes because women are more likely to report health issues.
“Data from randomised controlled trials suggest that most reactions following influenza vaccinations are mild, self-limited, and rarely serious. However, as the experience of an adverse event could be a barrier for subsequent vaccinations, limiting the impact of safety concerns on vaccination programme success is critical, especially for the influenza vaccine which is needed annually,” they write.
They add: “Transparent communication regarding the increased risk for females would potentially help sustain long-term trust in health authorities and vaccines.”
Kiely M, Tadount F, Lo E et al. Sex differences in adverse events following seasonal influenza vaccines: a meta-analysis of randomised controlled trials. Journal of Epidemiology & Community Health. 29 September 2023; doi 10.1136/jech-2023-220781
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