Receiving COVID-19 and flu vaccines at the same visit resulted in no increase in moderate or severe side effects, according to a recent clinical trial.

This randomized, placebo-controlled clinical trial evaluated the safety and reactogenicity of simultaneous versus sequential administration of mRNA COVID-19 and inactivated influenza vaccines. Conducted at three U.S. sites, the study included 335 nonpregnant participants aged 5 years or older (mean age, 33.4 years), who were randomized to receive both vaccines either simultaneously or sequentially with a 1- to 2-week interval. The primary outcome was the proportion of participants experiencing moderate to severe reactions, such as fever, chills, myalgia, or arthralgia, within 7 days post-vaccination.

Results, published in JAMA Network Open, showed that 25.6% of participants in the simultaneous group reported at least one moderate or severe reaction, compared to 31.3% in the sequential group, meeting the trial’s noninferiority margin (site-adjusted difference: -5.6 percentage points; 95% CI, -15.2 to 4.0 percentage points). Rates of unsolicited adverse events were also comparable between groups, with 12.4% in the simultaneous group and 9.6% in the sequential group. Serious adverse events occurred rarely, with only one case in each group, neither of which was related to the vaccinations.

Health-related quality of life (HRQOL), assessed using the EQ-5D-5L Index, showed a transient decrease in participants with severe reactions, from 0.92 to 0.81 post-vaccination, with scores returning to baseline within days.

The findings indicate that simultaneous administration of mRNA COVID-19 and influenza vaccines does not increase reactogenicity and aligns with the Centers for Disease Control and Prevention’s guidance on co-administration during peak viral seasons.

Full disclosures are available in the published study.