No increased risk for appendicitis reported with mRNA COVID-19 vaccination

The risk for appendicitis is not increased in association with mRNA COVID-19 vaccination or with diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), according to a research letter published online April 25 in JAMA Internal Medicine.

Helene Kildegaard, M.D., from the University of Southern Denmark in Odense, and colleagues used Danish nationwide registers to examine the risk for appendicitis after receipt of an mRNA COVID-19 vaccination and after diagnosis of SARS-CoV-2 infection.

The researchers found that among 4,048,883 individuals immunized with mRNA COVID-19 vaccines, there were 330 episodes of appendicitis within 21 days of the first dose, corresponding to 8.1 episodes per 100,000 individuals vaccinated. After the second dose, the rate was 8.6 per 100,000 individuals vaccinated (340 cases among 3,944,408 individuals). There was no increased risk for appendicitis observed after mRNA vaccination compared with the unvaccinated reference group (adjusted risk ratios, 0.93 [95 percent confidence interval, 0.79 to 1.11] after the first dose and 0.99 [95 percent confidence interval, 0.84 to 1.18] after the second dose). Across age groups, sexes, and vaccine types, this null association was stable. The adjusted risk ratio was 1.25 (95 percent confidence interval, 0.79 to 1.99) in analyses of the risk for appendicitis after SARS-CoV-2 infection versus the unvaccinated reference group.

"Further studies from different settings will be needed to fully eliminate appendicitis as an mRNA COVID-19 vaccination safety concern," the authors write.

Two authors disclosed financial ties to the pharmaceutical industry.