Study linking data from 85% of children in England compares rare cardiac risks post-COVID vs vaccination

A new study shows children and young people faced long-lasting and higher risks of rare heart and inflammatory complications after COVID-19 infection, compared to before or without an infection. Meanwhile COVID-19 vaccination was only linked to a short-term higher risk of myocarditis and pericarditis.

Published in The Lancet Child and Adolescent Health, the study is the largest of its kind in children and young people. It was led by researchers at the Universities of Cambridge and Edinburgh, University College London, and Great Ormond Street Hospital with support from the BHF Data Science Centre at Health Data Research UK.

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.

Co-author Professor Pia Hardelid, UCL and co-theme lead at the National Institute of Health and Care Research Great Ormond Street Hospital Biomedical Research Centre (NIHR GOSH BRC), 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.”

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.

Katherine Brown, co-author and professor of paediatric cardiac intensive care at GOSH, said: “This study helps us to understand the relationship between childhood covid infections and several different types of important acquired health problems in children (for example, thrombosis events, inflammatory diseases), in particular when these are more likely to happen. Although thrombosis events in children are very rare, when they happen, these can cause significant health problems for the affected child. 

“The study can help us to consider and weigh up risks for children who are undergoing heart operations, if they have experienced a recent covid infection. The study data may help us to plan major cardiac interventions on an individual basis and time treatment when the risk is lowest for the individual child.”

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.”