A US review of more than 245,000 doses of mRNA COVID vaccines given to young children – including those aged 4 and younger – found no indications of serious side effects.
Information regarding COVID vaccine safety among children under age 5 is limited and this is the first analysis to look for serious side effects from the mRNA vaccines in this cohort.
The study, published 6 June 2023 in Paediatrics, was led by the Kaiser Permanente Division of Research in partnership with the CDC, using data from the Vaccine Safety Datalink (VSD), which included paediatric records from 201 EDs, 105 UCCs, and 164 hospitals from nine network partners across 10 US states.
The researchers examined patient records from June 2022 to March 2023 for outcomes such as blood clots, stroke and brain inflammation among 135,005 doses of Pfizer given to children aged 6 months to 4 years, and 112,006 doses of the Moderna vaccine given to children aged 6 months to 5 years.
Lead author Dr Kristin Goddard said that, importantly, there was no indication of myocarditis among the children.
“We haven’t seen any myocarditis or pericarditis in this youngest age group, which is very reassuring,” Dr Goddard said.
“This interim analysis of children aged 5 years and younger, safety surveillance of more than 245,000 COVID mRNA vaccine doses over 9 months did not detect a safety signal for any outcome during the 21 days after vaccination.”
Her co-author and Director of the Centre, Professor Nicola Klein, noted that the study also revealed no safety concerns for seizures after vaccination, something occasionally seen following other routine childhood immunisations in children.
“Parents can be assured that this large study found no serious side effects from the mRNA vaccines and can protect their young children from COVID in the same way they vaccinate their children to protect from other serious childhood diseases,” she said.
The rate ration for convulsions and seizures for up to seven days post vaccination was 0.64 after Pfizer-BioNTech and 0.85 after Moderna.
One case of haemorrhagic stroke and one case of pulmonary embolism were identified after vaccination. However, a chart review found each outcome was unrelated to vaccination (both children had congenital abnormalities).
One case of anaphylaxis, found to be caused by a food allergy, was also recorded during the study period.
The team’s previous research published just a month earlier – also in Paediatrics – focussed on children aged 5 to 17-years-old and evaluated the vaccine effectiveness of BNT162b2 against mild to moderate and severe COVID.
“Even as the COVID emergency has ended, we know that the coronavirus poses a long-term, serious threat to all ages, including children,” Professor Klein said.
“We compared cases versus controls with respect to their demographic characteristics and comorbidities.”
There were 80,032 ED CLI associated encounters among children aged 5 to 17 years from April 9, 2021, to September 2022, of which 7,294 (74%) of 9,800 cases were unvaccinated, and 44,371 (63%) of 70,232 controls were unvaccinated.
Of these cases, 28% and 32% occurred during Delta, respectively, with 71% and 67% occurring during Omicron.
Among 17,998 CLI-associated ED encounters in adolescents aged 16 to 17 years, vaccine effectiveness (VE) during the Delta period was 93% from 14 to 59 days after dose two and decreased to 72% after 150 days.
Among 30,321 encounters in adolescents aged 12 to 15 years, VE was 93% from 14 to 59 days after dose two and decreased to 77% after 150 days; while during Omicron, VE from 14 to 59 days after dose two was 64% (44% to 77%) but decreased to 13% (3% to 23%) after 150 days.
However, VE in this cohort subsequently increased to 54% (40% to 65%) seven days after a monovalent booster dose.
Among the 31,713 CLI-associated ED/UC encounters in children aged 5 to 11 years, VE was 49% (33% to 61%) 14 to 59 days after two doses and 41% (29% to 51%) after 150 days.
“Although we could not measure VE in 5 to 11-year-olds before Omicron predominance, VE against ED/UC encounters during Omicron was similar across age groups, suggesting that the 10mcg per dose in children provided similar protection to the 30mcg per dose in older individuals,” Professor Klein explained.
“Further, 83% of our SARS-CoV2 positive hospitalisations were among unvaccinated patients, which, together with other reports, provides evidence that BNT162b2 offers protection against severe disease in children and adolescents.
“However, increased vaccine uptake is essential to optimise protection in this population.”