A large, multi-centre study led by researchers from UCL, Cambridge and Edinburgh analysed health records for about 13.9 million people under 18, spanning 1 January 2020 to 31 December 2022. The study found that the Pfizer-BioNTech Covid-19 vaccine caused far fewer problems than infection itself in children and young people. The researchers noted that the health risks seen after infection lasted longer than those following vaccination. They also observed that most myocarditis or pericarditis cases after vaccination occurred within a week and were more common in boys under 25.

The team examined rare outcomes such as thrombocytopenia, arterial and venous thrombosis, as well as myocarditis and pericarditis. They found a higher risk of these conditions in the 12 months after a Covid-19 diagnosis than after vaccination. The risk of myocarditis or pericarditis was higher in the first four weeks after vaccination, but substantially lower than after infection. Dr Alexia Sampri of Cambridge said the findings show that while such conditions are rare, the likelihood of heart, vascular or inflammatory problems was higher after a Covid infection than after vaccination, and infection-related risks tended to persist longer.

Co-authors Prof Angela Wood of Cambridge and Prof William Whiteley of Edinburgh noted findings on inflammatory conditions such as paediatric inflammatory multisystem syndrome (PIMS) and Kawasaki disease. Wood said that after a Covid-19 diagnosis the risk of these conditions was around 15-fold higher in the early weeks and remained elevated for many months, whereas after vaccination the risk was near background levels. Whiteley added that hospital and GP data help provide a complete picture for public health decisions. The Lancet Child and Adolescent Health published the study, which researchers say matters for policymakers and caregivers as they consider vaccination for children and young people. They emphasised that vaccine-related risks are rare and short-lived, while infection risk could evolve with new variants.