649 
The safety of Covid-19 mRNA vaccines when used in children under five years of age has been reassured following a recent analysis of nearly a quarter of million doses.
Published in the journal Pediatrics, US researchers analysed information contained within the Vaccine Safety Datalink (VSD) on the use of mRNA vaccines in children aged five years of age and younger.
The VSD is a collaborative effort between the Centers for Disease Control and Prevention and eight data-contributing health systems. It maintains comprehensive electronic medical records for members, including Covid-19 vaccination data from retail pharmacies and state immunisation registries.
The researchers examined a total of 23 pre-specified safety outcomes including myocarditis, pericarditis and seizures. The primary analyses compared the incidence of these safety outcomes during a pre-specified risk interval (one to 21 days post-vaccination) with outcomes among primary series vaccinated comparators who were less recently vaccinated at 22-42 days post-vaccination.
Incidence of mRNA vaccine safety outcomes
In total, 135,005 doses of the Pfizer-BioNTech Covid-19 vaccine and 112,006 doses of the Moderna Covid-19 vaccine (i.e. mRNA vaccines) were given to children aged six months to five years in the VSD population. The risk ratios were not elevated for any of the pre-specified safety outcomes following any dose of either mRNA vaccine. As an example, the risk ratios for convulsions and seizures in zero to seven days post-vaccination were 0.64 (95% CI 0.25 – 1.51, p = 0.89) for Pfizer-BioNTech and 0.85 (95% CI, 0.27 – 2.32, p = .70) after Moderna.
The researchers concluded that these ongoing surveillance data should provide reassurance to clinicians, parents and policymakers.
Reassuring results
A previous interim analysis concluded that the incidence of selected serious outcomes was not significantly higher one to 21 days post-vaccination compared with 22-42 days post-vaccination for mRNA Covid-19 vaccines. Moreover, a further analysis indicated a low incidence of myocarditis and pericarditis among individuals persons aged five to 39 years. While these data are reassuring, further safety monitoring data are needed for mRNA doses, particularly when administered to children aged six months to five years of age, hence the current study.
