Female recipients, especially those ages 31 to 45 years, of the Moderna COVID-19 vaccine (messenger ribonucleic acid [mRNA]-1273 SARS-CoV-2) are more likely to develop a benign, late-onset, pruritic rash at the injection site compared with their male counterparts or recipients of the Pfizer COVID-19 vaccine (BNT162b), according to study results published in Clinical Infectious Diseases. However, this rash does not lead to serious sequelae and should not hinder individuals from receiving the second vaccine dose.

A team of investigators conducted an observational cohort study of hospital workers at San Francisco General Hospital in California to characterize clinical features, incidence, and demographics associated with injection site rash among employees who received their first SARS-CoV2 mRNA vaccine.

Of the employees who received their first vaccine between December 14, 2020, and January 8, 2021, 1955 hospital workers (1275 women; 675 men) received the Moderna COVID-19 vaccine and 3612 (2350 women; 1249 men) received the Pfizer COVID-19 vaccine.


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The cumulative incidence of delayed injection site reaction to either the first or second dose among female employees who received their first dose of the Moderna COVID-19 vaccine was 1.1%. In a subgroup of 557 female employees aged 31 to 45 years, the incidence was 2.0%. Delayed injection site reactions were not reported among any male employees who received the Moderna COVID-19 vaccine nor among any recipients of the Pfizer COVID-19 vaccine.

A total of 13 female workers (aged 28 to 55 years) who received the Moderna COVID-19 vaccine reported experiencing a delayed injection site reaction with erythema and pruritus, the onset of which was noted 3 to 9 days (median 7 days) after the first dose of the Moderna COVID-19 vaccine. After the second dose, 5 female employees had milder or similar reactions with earlier onset, and 1 woman reported this delayed reaction only after receiving the second dose.

“[As] an estimated 30 million American women in the 31-45 age group are eligible for vaccination to prevent COVID-19, it is imperative to accurately define the characteristics of these reactions and reassure the public that they resolve within a week and are not associated with medically significant adverse events,” the investigators noted.

“More research is needed to characterize the epidemiology, immunologic mechanism, prevention, and treatment of delayed injection site reactions to mRNA-based vaccines and why the delayed injection site reaction that we and others have observed has a predilection for females,” concluded the authors.

Reference

Jacobson MA, Zakaria A, Maung Z, et al. Incidence and characteristics of delayed injection site reaction to the mRNA-1273 SARS-CoV-2 vaccine (Moderna) in a cohort of hospital employees. Clin Infect Dis. Published online June 4, 2021. doi:10.1093/cid/ciab518

This article originally appeared on Infectious Disease Advisor