COVID-19 mRNA vaccines given to young children (most of them age 4 and younger) are safe and showed no indications of serious side effects, according to a review of more than 245,000 doses.

The study marks the first analysis looking for serious side effects from the mRNA vaccines in young children.

Researchers from Kaiser Permanente and the US Centers for Disease Control and Prevention (CDC) examined patient records from June 2022 to March 2023 for both the Pfizer and Moderna vaccines.

The results, published in the journal Paediatrics, showed that there was no indication of heart inflammation called myocarditis among the young vaccinated children.

"We haven't seen any myocarditis or pericarditis in this youngest age group, which is very reassuring," said lead author Kristin Goddard, MPH, research project manager with the Kaiser Permanente Vaccine Study Center.

Myocarditis has emerged as a rare side effect of COVID vaccination, mostly among teenage or young adult men.

The team examined medical records for 23 serious potential side effects, including outcomes such as blood clots, seizures, stroke, and brain inflammation.

Analyses showed no safety concerns for any of the selected serious side effects. In particular, the study found no concern for seizures after vaccination, something occasionally seen following other routine childhood immunisations in children under 2 years old.

Meanwhile, the CDC previously reported mild side effects from immunisation, such as sore arms or brief fevers. The analysis covered a large and diverse group of children. It included 135,005 doses of the Pfizer COVID-19 vaccine given to children aged 6 months to 4 years and 112,006 doses of the Moderna COVID-19 vaccine given to children aged 6 months to 5 years.

"Parents can be assured that this large study found no serious side effects from the mRNA vaccines," said senior author Nicola Klein, director of the Kaiser Permanente Vaccine Study Center and research scientist with the Division of Research.

While the COVID-19 emergency has ended, the coronavirus still poses a long-term, serious threat to all ages, including children

"Vaccinating children against COVID-19 benefits them by reducing the burden of illness, avoiding spreading the virus to family and others, and mitigating the small but real risk of serious illness," Klein added.