Infection-Linked Vascular Risks Persist in Children After COVID-19 Infection, Vaccine-Related Risks Are Short-Term

Key Highlights

• COVID-19 infection was associated with rare but notable increases in thromboembolic, hematologic, cardiac, and inflammatory events—some persisting up to 1 year.
• The most common postinfection complications were venous thromboembolism, thrombocytopenia, myocarditis or pericarditis, and multisystem inflammatory conditions.
• After vaccination, myocarditis or pericarditis was rare, short-term, and significantly less frequent than after infection.

A retrospective, population-based cohort study published in The Lancet Child & Adolescent Health used linked electronic health records across England to examine vascular and inflammatory outcomes following COVID-19 infection and BNT162b2 vaccination in children and young people. The analysis provides comparative evidence on the frequency, timing, and duration of postinfection and postvaccination risks.

Researchers analyzed nationwide electronic health records for all individuals younger than 18 years in England between January 2020 and December 2022. Two cohorts were established: one tracking the first recorded COVID-19 diagnosis (January 2020–March 2022) and another evaluating the first BNT162b2 (Pfizer–BioNTech) vaccination (August 6, 2021–December 31, 2022) among children aged 5 to 17 years.

The study assessed arterial and venous thrombotic events (VTE), thrombocytopenia, myocarditis or pericarditis, and systemic inflammatory conditions. Adjusted hazard ratios (aHRs) were estimated for defined intervals following infection or vaccination, controlling for potential confounders including age, sex, ethnicity, region, socioeconomic deprivation, general practitioner contact frequency, and recent medication use.

To measure the cumulative burden of these events, investigators calculated 6-month absolute excess risks (AERs) using life-table modeling. This approach allowed direct comparison of short- and long-term vascular and inflammatory outcomes after infection versus vaccination in children and young people.

Study Findings

Among 13,896,125 individuals, 3,903,410 (28.1%) had a COVID-19 diagnosis. In week 1 postdiagnosis, risks rose sharply versus no/before diagnosis: arterial thromboembolism (aHR 2.33 [95% CI 1.20–4.51]), venous thromboembolism (aHR 4.90 [95% CI 3.66–6.55]), thrombocytopenia (aHR 3.64 [95% CI 2.21–6.00]), myocarditis or pericarditis (aHR 3.46 [95% CI 2.06–5.80]), and inflammatory conditions (aHR 14.84 [95% CI 11.01–19.99]) (Table 1).

Table 1. Week 1 postdiagnosis risks compared with no/before diagnosis

Although incidence decreased after 4 weeks, relative risks for VTE, thrombocytopenia, and myocarditis/pericarditis remained elevated beyond 12 months. Over the first 6 months, the absolute excess risks (AERs) per 100,000 individuals aged 5–18 were 5.58 for VTE, 2.28 for thrombocytopenia, 2.24 for myocarditis/pericarditis, and 17.43 for inflammatory conditions. (Table 2).

Table 2. 6-month absolute excess risks (AERs) after first COVID-19 diagnosis (per 100,000 individuals aged 5–18)

Among 9,245,395 vaccine-eligible participants, 3,407,560 (36.9%) received a first BNT162b2 dose. Myocarditis or pericarditis risk was elevated within the first 4 weeks after vaccination (week-1 aHR 6.17 [4.24–8.96]; weeks 2–4 aHR 1.84 [1.25–2.72]) but not beyond that period. The 6-month AER for myocarditis or pericarditis was 0.85 (0.07–1.91) per 100,000—significantly lower than after infection.

Clinical Implications

For clinicians, these findings highlight that postinfection thromboinflammatory complications in children, though rare, can persist for months, underscoring the need for follow-up care after SARS-CoV-2 infection. By contrast, vaccine-related myocarditis or pericarditis was short-term, rare, and far less frequent than infection-related complications, supporting vaccination as a protective strategy.

Expert Commentary

“Children and young people have higher risks of rare vascular and inflammatory diseases up to 12 months after a first COVID-19 diagnosis and higher risk of rare myocarditis or pericarditis up to 4 weeks after a first BNT162b2 vaccine, although the risk following vaccination is substantially lower than the risk following infection,” the researchers noted in their study. “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.”

In this nationwide English cohort, COVID-19 infection was linked to significant but rare thromboinflammatory risks that persisted for up to a year, while vaccine-related myocarditis or pericarditis was infrequent and transient. The findings support continued vaccination in children and young people to mitigate the greater and longer-lasting risks associated with SARS-CoV-2 infection.

Reference
Sampri A, Shi W, Bolton T, et al. Vascular and inflammatory diseases after COVID-19 infection and vaccination in children and young people in England: a retrospective, population-based cohort study using linked electronic health records. Lancet Child Adolesc Health. 2025;9(12). doi:10.1016/S2352-4642(25)00247-0