Comparison of adverse reactions to COVID-19 XBB.1.5 and influenza vaccination in the 2023-24 Japanese influenza season

Introduction

Adverse reactions to the most recent XBB.1.5 monovalent COVID-19 and seasonal influenza vaccines administered from September to December in 2023 were compared.

Methods

Outpatients were administered the COVID-19 and/or influenza vaccine. Patients reported five local and six systemic solicited adverse reactions for seven days through a self-report diary. The data from 217 diaries for the COVID-19 vaccine and 140 diaries for the influenza vaccine were collected and analyzed, including 43 diaries from subjects who received both vaccines and recorded a diary, for a total of 357 diaries from 314 subjects.

Results

Among the systemic reactions, fatigue, headache, and myalgia were more frequent with the COVID-19 vaccine (p < 0.001, p < 0.01, p < 0.001, respectively). The local adverse reactions of redness and swelling were significantly more frequent with the influenza vaccine (p < 0.001 and p < 0.05, respectively). For both vaccines, most of the systemic and local reactions were less frequent in subjects 65 years or over than in those under 65. No significant increase in adverse reactions was observed for vaccinations within 14 days compared to those more than 14 days apart or the COVID-19 vaccine alone. Multiple regression analysis also showed that systemic reactions including fatigue, headache, and myalgia, to COVID-19 vaccine, were negatively correlated with age (p < 0.001, p < 0.001 and p = 0.005, respectively).

Conclusions

These findings suggest that there are significant differences between the COVID-19 and influenza vaccines in terms of the composition of the adverse reactions and there is a lower incidence of adverse reactions for persons 65 years or older.