A large study in the UK has reported that children and adolescents are at substantially more risk of developing heart inflammation, blood clots, and other vascular and inflammatory diseases after COVID-19 infection than after vaccination.
The study, published recently in The Lancet Child & Adolescent Health, drew on the health records of nearly 14 million individuals under 18 in England and provides the clearest evidence yet that the dangers of infection far outweigh the minimal and short-term risks associated with vaccines.
This retrospective, population-based cohort study, led by researchers from the University of Cambridge and supported by the Wellcome Trust, the British Heart Foundation, and Health Data Research UK, compared the short- and long-term risks of five groups of rare but serious conditions after the first COVID-19 diagnosis and after the first dose of the Pfizer-BioNTech BNT162b2 vaccine (a.k.a. Comirnaty). These conditions included arterial and venous thrombotic events, thrombocytopenia, myocarditis and pericarditis, and systemic inflammatory diseases such as paediatric multisystem inflammatory syndrome (MIS-C).
The researchers analysed anonymised medical records of over 58 million people and linked electronic health records covering almost all general practitioners and hospitals across England between January 2020 and December 2022. Of the 13.9 million children and adolescents studied, about 3.9 million had a documented COVID-19 diagnosis. At the same time, 3.4 million individuals aged 5-17 years had received at least one dose of the vaccine.
Risks after infection, vaccination
The results were striking. In the first week following infection, children and adolescents had sharply higher risk across every measured outcome compared to those never infected. The likelihood of systemic inflammatory conditions, including MIS-C, was nearly 15x higher than in uninfected peers. The risk of venous thromboembolism — clotting in the veins and lungs — was almost 5x higher; that of thrombocytopenia was over 3x higher; that of myocarditis and pericarditis showed a 3.5x rise; and that of arterial clotting events, such as stroke and heart attacks, were more than 2x as likely. While these elevations declined after the first few weeks, they didn’t disappear quickly. For venous thromboembolism, low platelet counts, and cardiac inflammation, the risk remained significantly above baseline even a year after infection.
In contrast, vaccination was associated with only one notable short-term effect: a mild increase in the risk of myocarditis and pericarditis in the first month after the dose. The risk peaked during the first week, when it was around 6x higher than average, but declined rapidly by the fourth week and showed no increase thereafter. There was no sign of elevated risk for blood clots, platelet changes or systemic inflammatory conditions after vaccination.
To put these figures into perspective, the researchers calculated absolute excess risk, i.e. the additional number of cases expected per 100,000 children within six months of infection or vaccination. Following infection, inflammatory diseases such as MIS-C were observed in roughly 17 per 100,000 children; venous clotting in about 5.6; and myocarditis or pericarditis in 2.2.
After vaccination, the excess risk of myocarditis or pericarditis was just 0.85 per 100,000, and negligible for other conditions. In other words, a child was about 3x more likely to develop cardiac inflammation after COVID-19 infection than after vaccination, and infection was also linked to a wider range of complications.
The persistence of certain complications months after recovery suggests an extended inflammatory or vascular response triggered by the virus. The researchers noted this may be linked to immune dysregulation or endothelial injury, mechanisms thought to underlie long COVID-19 and MIS-C. While arterial events such as stroke declined more quickly among children than adults, venous and inflammatory conditions lingered, implying age-related differences in how blood vessels and the immune system recovered after infection.
The researchers emphasised that the few cases of myocarditis after vaccination were mild and self-limiting. Most affected children recovered quickly with standard care and didn’t suffer lasting cardiac damage. While they observed a small, short-term rise in myocarditis following vaccination, the risk after COVID-19 infection was several times higher and persisted longer. Vaccination thus remains the safer, more effective way to protect children from serious post-COVID complications.
The authors wrote that their findings should reassure parents and policymakers weighing the benefits of vaccinating children. Children and young people have higher risks of rare vascular and inflammatory diseases up to 12 months after COVID-19 infection and a lower short-term risk after vaccination. These results support continued vaccination of children and adolescents to reduce the more frequent and longer-lasting risks associated with a SARS-CoV-2 infection.
Strengths and limitations
The scale of the data makes the study one of the most comprehensive analyses of paediatric COVID-19 outcomes to date. Covering 98% of England’s population, it linked information from primary care, hospitals, emergency services, pharmacy dispensing, laboratory testing, and mortality records — allowing researchers to capture even very rare outcomes such as MIS-C and pediatric thrombosis, which smaller studies would have missed.
The results also align with evidence from adult populations showing COVID-19 infections markedly increase clotting and inflammatory risks while vaccination confers significant protection.
Nevertheless, the authors acknowledged certain limitations. Some infections early in the pandemic may have gone undetected due to limited testing, leading to an underestimation of infection-related risks. Diagnoses drawn from health records may not capture every mild case, and the study didn’t evaluate repeated infections or multiple vaccine doses. However, these factors are unlikely to change the overall conclusion: the infection carries greater and more prolonged risks than vaccination.
Public health significance
Public health experts have welcomed the findings, noting their importance at a time when vaccine hesitancy remains among some parents. During the pandemic, reports of myocarditis following mRNA vaccination in older children and adolescents had prompted caution in several countries, temporarily delaying recommendations for younger age groups. This new evidence, based on millions of real-world records, shows that the infection itself poses a far greater danger to children’s hearts, blood vessels, and immune systems than the vaccine ever did.
The researchers also observed a possible weakening of infection-related risks over successive pandemic waves, likely reflecting changes in circulating variants and higher acquired immunity in the population. Yet even during later periods, children with COVID-19 remained at measurably higher risk of vascular and inflammatory complications than their uninfected peers.
Clarity amid confusion
Taken together, the study has underscored a simple but crucial public health message: while children often experience only mild acute COVID-19, the infection can leave behind rare but serious complications that last for months. Vaccination on the other hand carries a minimal and short-lived risk.
In a public health landscape still shaped by the long tail of the pandemic, the findings offer clarity amid confusion. COVID-19 infection in children is not without consequence: it carries measurable risks to the cardiovascular and immune systems that can remain long after the virus has cleared — whereas vaccination presents a vanishingly small and short-lived hazard.
Vipin M. Vashishtha is director and paediatrician, Mangla Hospital and Research Center, Bijnor.
Published – November 21, 2025 08:30 am IST
