Data: Risks of vascular, inflammatory conditions in kids higher after COVID infection than vaccination

COVID-19
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Rare vascular and inflammatory conditions such as blood clots, myocarditis, and pericarditis occur more often in children after COVID-19 infection than after vaccination against the disease, UK researchers suggest in a study published in The Lancet Child & Adolescent Health.

The largest of its kind, the study analyzed linked electronic health records for nearly all (13.9 million) children in England. In total, 28.1% had a COVID-19 diagnosis from January 2020 to December 2022, and 36.9% of eligible children were vaccinated from August 2021 through December 2022.

Roughly half (48.8%) of participants were girls, 33.7% were aged 0 to 4 years, 36.4% were 5 to 11 years, 29.9% were 12 to 17, 71.7% were White, 12.1% were South Asian, 5.4% were Black, and 4.7% were mixed race.

Informed parental decision-making

The study evaluated rates of short- and long-term risks of rare complications, including arterial and venous thrombosis (blood clots), thrombocytopenia (low platelet levels in the blood), myocarditis or pericarditis (inflammation of the heart or its surrounding tissue, respectively), and inflammatory conditions after COVID-19 diagnosis or vaccination.

The research was led by scientists at the University of Cambridge, the University of Edinburgh, and University College London and supported by the BHF Data Science Centre at Health Data Research UK.

"Parents and carers have faced difficult choices throughout the pandemic," coauthor Pia Hardelid, of the National Institute of Health and Care Research Great Ormond Street Hospital Biomedical Research Centre, said in a Health Data Research UK press release. "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."

Post-COVID event risks higher for over 1 year

During the study period, 3.9 million children had COVID-19 for the first time, and 3.4 million aged 5 to 18 years received their first Pfizer/BioNTech COVID-19 vaccine. 

Among infected children during 15 months of follow-up, researchers calculated event rates per 100,000 person-years of 5.26 for arterial thromboembolism, 10.64 for venous thromboembolism, 8.40 for thrombocytopenia, 4.47 for myocarditis or pericarditis, and 8.05 for systemic inflammatory conditions.

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. 

Angela Wood, PhD

Over 17 months of follow-up among vaccinated participants, event rates per 100,000 children were 5.24 for arterial thromboembolism, 13.30 for venous thromboembolism, 7.94 for thrombocytopenia, 6.94 for myocarditis or pericarditis, and 6.90 for inflammatory conditions. 

Relative to no diagnosis, COVID-19 diagnosis was associated with higher risks of arterial thromboembolism (adjusted hazard ratio [aHR], 2.33), venous thromboembolism (aHR, 4.90), thrombocytopenia (aHR, 3.64), myocarditis or pericarditis (aHR, 3.46), and inflammatory conditions (aHR, 14.84) in the first week after diagnosis. 

Incidence of these conditions fell from weeks 2 to 4 but stayed elevated for more than 1 year for venous thromboembolism (aHR, 1.39), thrombocytopenia (aHR, 1.42), and myocarditis or pericarditis (aHR, 1.42). 

COVID-19 vaccination was tied to an elevated risk of myocarditis or pericarditis, but only in the first month after vaccination (aHR, 1.84). Over 6 months, COVID-19 infection led to 2.24 extra cases of myocarditis or pericarditis per 100,000 children, compared with 0.85 extra cases per 100,000 children after vaccination.

"These findings are of great importance for national policy makers and caregivers considering vaccination consent for children, and support the public health strategy of COVID-19 vaccination in children and young people to mitigate the more frequent and persistent risks associated with SARS-CoV-2 infection," the researchers concluded.

In the press release, coauthor Angela Wood, PhD, of the University of Cambridge, said, "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."

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