Abstract
IMPORTANCE: A delayed large local reaction (DLLR) is a delayed-onset adverse skin reaction that may occur after injection of the mRNA-1273 vaccine against SARS-CoV-2. OBJECTIVE: To examine the associations between sex and age and susceptibility of DLLRs after mRNA-1273 vaccination. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cross-sectional study was conducted at the Self-Defense Forces large-scale vaccination center in Tokyo, Japan, from May 24 to November 30, 2021. Participants were recipients of the second dose of the mRNA-1273 vaccine who had received the first dose 4 to 6 weeks earlier. Five experienced dermatologists interviewed participants to assess whether they had experienced symptoms of DLLR after administration of the first dose of the vaccine. EXPOSURE: Receipt of the first dose of the mRNA-1273 vaccine. MAIN OUTCOMES AND MEASURES: The primary outcome was the incidence rate of DLLR stratified by sex and age group. Odds ratios (ORs) were calculated to evaluate the differences between groups. Outcomes were tested for significance using the Pearson χ2 test with 95% CIs. RESULTS: Of 5893 participants in the study, 3318 (56.3%) were male (median age, 55 years [IQR, 38-68 years]) and 2575 (43.7%) were female (median age, 50 years [IQR, 34-67 years]). A total of 747 participants (12.7%) experienced DLLR symptoms after the first dose of the mRNA-1273 vaccine. Symptoms were mild and not considered as contraindications to the vaccine. The incidence rate was significantly higher among females (22.4% [577 participants]; OR, 5.30; 95% CI, 4.42-6.34) than among males (5.1% [170 participants]; reference). Moreover, the incidence rate was significantly higher among participants aged 30 to 39 years (14.3% [129 participants]; OR, 1.68; 95% CI, 1.25-2.26), 40 to 49 years (15.8% [136 participants]; OR, 1.89; 95% CI, 1.41-2.53), 50 to 59 years (14.9% [104 participants]; OR, 1.76; 95% CI, 1.29-2.40), and 60 to 69 years (12.6% [182 participants]; OR, 1.45; 95% CI, 1.10-1.91) than among participants aged 18 to 29 years (9.0% [81 participants]; reference). CONCLUSIONS AND RELEVANCE: In this cross-sectional study, the first dose of the SARS-CoV-2 mRNA-1273 vaccine was associated with a higher incidence of DLLR among females and among individuals aged 30 to 69 years. The findings suggest that DLLR may be a type IV allergic skin reaction.