For years, the global conversation around COVID-19 has focused on its immediate effects—how it spreads, how to treat it, and how vaccines protect against it. But as the world turns its gaze toward recovery, science continues to reveal how the virus can leave quiet, lasting imprints, especially in the youngest among us. A groundbreaking study published in The Lancet Child and Adolescent Health has now provided the clearest picture yet of how COVID-19 infection affects the hearts and vascular systems of children and young people—and how those risks compare with vaccination.
The findings are both reassuring and sobering. While complications like myocarditis and pericarditis—types of heart inflammation—remain rare, the study shows that the risks of such conditions are significantly higher and longer-lasting after a COVID-19 infection than after vaccination. In contrast, any increased risk linked to vaccination appears to be short-term and fades within weeks.
A Landmark Study of Nearly 14 Million Children
This research represents one of the largest and most comprehensive studies ever conducted on the pediatric population during the pandemic. Led by scientists from the Universities of Cambridge and Edinburgh and University College London, the project drew on electronic health records (EHRs) covering almost 14 million children and young people in England under the age of 18.
The study examined data from January 2020 to December 2022, a period that spans the rise of multiple COVID-19 variants and the rollout of vaccines. Of the children analyzed, around 3.9 million had a confirmed COVID-19 diagnosis, while 3.4 million received the Pfizer–BioNTech (BNT162b2) vaccine—the main vaccine used in this age group during the study.
To ensure privacy and accuracy, all identifying information was removed. Researchers conducted their analyses within NHS England’s Secure Data Environment (SDE), a safeguarded digital system that allows for sensitive health data to be studied responsibly and ethically.
What the Researchers Found
The study focused on five rare but potentially serious complications: arterial and venous thrombosis (blood clots in arteries or veins), thrombocytopenia (low platelet counts), myocarditis (inflammation of the heart muscle), pericarditis (inflammation of the heart’s outer lining), and other inflammatory conditions.
The results were striking. After a first COVID-19 diagnosis, the risks for all five complications were highest during the first month—but for several of these conditions, the elevated risk persisted for up to a year. Children and young people who had been infected were more likely to experience lingering heart, vascular, or inflammatory problems compared to those who had not been infected.
In contrast, after COVID-19 vaccination, researchers observed only a short-term increase in the risk of myocarditis or pericarditis during the first four weeks. After that period, the risk returned to baseline levels. No long-term elevation in risk was found for any of the other conditions.
Quantitatively, the difference was clear. Over a six-month period, COVID-19 infection was linked to roughly 2.24 additional cases of myocarditis or pericarditis per 100,000 children and young people. Among those vaccinated, only 0.85 additional cases per 100,000 were observed.
These numbers highlight a crucial fact: while both infection and vaccination can carry risks, those associated with infection are not only higher but endure much longer.
The Significance of the Findings
For parents, educators, and healthcare professionals, these results offer vital clarity in a landscape often clouded by uncertainty and misinformation. Principal author Dr. Alexia Sampri of the University of Cambridge explained, “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.”
This finding aligns with earlier research suggesting that the virus itself, not the vaccine, poses the greater threat to heart health. Previous studies have shown that even mild COVID-19 infections can trigger inflammation throughout the body, affecting not just the lungs but also the cardiovascular system. The immune system’s overreaction, sometimes referred to as “cytokine storms,” can lead to damage in tissues including the heart and blood vessels.
By contrast, vaccine-related myocarditis—though it can occur, particularly among young males after mRNA vaccines—is typically mild, short-lived, and resolves quickly with proper care.
Building an Evidence Base for Families and Clinicians
Throughout the pandemic, parents have faced agonizing choices about whether to vaccinate their children, often amid conflicting information. Professor Pia Hardelid, co-author from University College London, acknowledged this reality, emphasizing the study’s goal of providing reliable, balanced evidence. “Parents and caregivers 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,” she said.
This evidence doesn’t just help families—it also informs national health policies. Professor Angela Wood of the University of Cambridge, another co-author, noted how the scale of the study enables the identification of even the rarest complications. “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.”
She also cautioned that the situation could evolve as new COVID-19 variants emerge and population immunity changes. “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.”
The Role of Data in Protecting Public Health
This study underscores the immense value of linked health data in understanding real-world effects on large populations. By integrating hospital and general practice data across the NHS, scientists were able to observe patterns that would otherwise remain invisible.
Professor William Whiteley from the University of Edinburgh emphasized that this kind of evidence is essential for trust and informed decision-making. “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 they tell us what has happened to people looked after in the NHS.”
He added that the overall message is reassuring: “Risks of myocarditis and inflammatory illnesses were low for children and young people, and they were lower after COVID-19 vaccination than after COVID-19 infection.”
Why This Matters for the Future
Beyond the immediate implications, the study raises deeper questions about how we understand long-term health risks in the aftermath of a pandemic. While vaccines have proven to be powerful tools in reducing severe illness and hospitalizations, the virus continues to evolve—and so too must our understanding of its effects.
The persistence of elevated risks for heart and inflammatory conditions months after infection suggests that COVID-19 can act like a stone dropped in water, sending ripples long after the initial splash. For children and young people—many of whom may experience only mild symptoms initially—this research is a reminder that “mild” infection does not always mean “harmless.”
At the same time, the study offers a hopeful message. Vaccination not only reduces the likelihood of severe disease but also appears to minimize the risk of these rare yet serious complications in the long run. It demonstrates how science, through rigorous and transparent study, continues to illuminate the path toward safer, better-informed public health choices.
A Clearer Picture, A Safer Tomorrow
Science thrives on clarity, and this study brings it in abundance. The message is not one of fear but of understanding: the risks of heart and inflammatory complications remain rare in children and young people, but when they occur, they are more often a result of infection than vaccination.
As the world learns to live with COVID-19, studies like this help ensure that our decisions—whether personal or policy-level—are shaped by evidence, not uncertainty. The findings remind us that every data point represents a real child, a real family, a real heartbeat.
And for parents, healthcare providers, and scientists alike, that heartbeat is what matters most.
More information: 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, The Lancet Child & Adolescent Health (2025). DOI: 10.1016/S2352-4642(25)00247-0
