The study is the largest of its kind in this population, and is published in The Lancet Child and Adolescent Health . It was led by scientists at the Universities of Cambridge and Edinburgh, and University College London, with support from the BHF Data Science Centre at Health Data Research UK.
Principal author Dr Alexia Sampri, University of Cambridge, said:
"Our whole-population study during the pandemic showed that although these conditions were rare, children and young people were more likely to experience heart, vascular or inflammatory problems after a COVID-19 infection than after having the vaccine — and the risks after infection lasted much longer."
The research team uncovered these findings by analysing linked electronic health records (EHRs) for nearly 14 million children in England under the age of 18 between 1 January 2020 and 31 December 2022, covering 98% of this population. During this period, 3.9 million children and young people had a first COVID-19 diagnosis. And 3.4 million had a first COVID-19 BNT162b2 (Pfizer–BioNTech) vaccine, the main vaccine used in 5-18-year-olds during the study period.
All personal information that could identify individuals had been stripped away, and approved researchers accessed this data entirely within the NHS England Secure Data Environment (SDE), a secure data and analysis platform.
The study looked at short- and long-term risks of rare complications including arterial and venous thrombosis (clots in blood vessels), thrombocytopenia (low levels of platelets in the blood), myocarditis or pericarditis (inflammation of the heart and its surrounding tissue respectively), and inflammatory conditions after COVID-19 diagnosis or vaccination.
After a first COVID-19 diagnosis, risks of the five conditions studied were highest in the first four weeks and, for several conditions, stayed higher for up to 12 months, compared to children and young people without or before a diagnosis.
In contrast, after COVID-19 vaccination, the team only saw a short-term higher risk in myocarditis or pericarditis in the first four weeks, compared to children and young people without or before vaccination. After that, the risk returned to the same level as the start of the study period.
Over six months, the research team estimated that COVID-19 infection led to 2.24 extra cases of myocarditis or pericarditis per 100,000 children and young people who had COVID-19. In those who were vaccinated, there were only 0.85 extra cases per 100,000 children and young people.
Previous research showed that children and young people diagnosed with COVID-19 are at a higher risk of developing conditions like myocarditis, pericarditis, and thrombocytopenia, compared to their peers who hadn't had a COVID-19 diagnosis.
While many studies show that COVID-19 vaccines can help children to avoid severe illness and hospitalisation, some also report rare cases of myocarditis in young people shortly after receiving a COVID-19 vaccine, particularly for mRNA-based vaccines.
However, there hasn't been any research directly comparing the longer-term risks of both COVID-19 diagnosis and vaccinations in children and young people until now.
Co-author Professor Pia Hardelid, UCL and National Institute of Health and Care Research Great Ormond Street Hospital Biomedical Research Centre, said:
"Parents and carers have faced difficult choices throughout the pandemic. By building a stronger evidence base on both infection and vaccination outcomes, we hope to support families and healthcare professionals to make decisions grounded in the best available data."
Co-author Professor Angela Wood, University of Cambridge and Associate Director at the BHF Data Science Centre, said:
"Using electronic health records from all children and young people in England, we were able to study very rare but serious heart and clotting complications, and found higher and longer-lasting risks after COVID-19 infection than after vaccination. Whilst vaccine-related risks are likely to remain rare and short-lived, future risks following infection could change as new variants emerge and immunity shifts. That's why whole-population health data monitoring remains essential to guide vaccine and other important public health decisions."
Co-author Professor William Whiteley, University of Edinburgh and Associate Director at the BHF Data Science Centre, said:
"Parents, young people, and children need reliable information to make decisions about their health. Data from hospitals and GP practices are an important part of the picture because tell us all what has happened to people looked after in the NHS. Here we have shown that during the pandemic, risks of myocarditis and inflammatory illnesses were low for children and young people, and that they were less after COVID-19 vaccination than after COVID-19 infection."
