Thread by @ZdenekVrozina

A new study in The Lancet Child & Adolescent Health followed nearly 14 million children in England.
It shows that SARS-CoV-2 infection leaves long-term marks on the vascular and immune system - even in kids.
Not just for weeks, but measurable up to a year later🧵

https://twitter.com/yash25571056/status/1986027562435289208

After COVID-19, children had a sharply increased risk of
systemic inflammatory syndromes (MIS-C, etc)
venous thrombosis
thrombocytopenia
myocarditis and pericarditis
And part of these risks remained elevated 12 months post-infection.

That means - even if a child feels fine after COVID, the body may stay in a dysregulated immune and vascular state - with lingering inflammation and endothelial stress.
In biological terms, COVID leaves a footprint

Mechanisms are consistent with what we see in adults
endothelial injury,
microcirculatory dysfunction,
coagulation changes,
viral antigen persistence.
Together, they explain why a mild infection doesn’t always mean a harmless one.

This study covers Jan 2020 - Mar 2022, ie mainly the Alpha and Delta waves.
That’s key - those variants triggered the strongest vascular and inflammatory responses.
Omicron infections were only starting to appear by the end of the study window.

But newer data are in.
A Nature Communications 2025 study following children and adolescents in the Omicron era confirms that infection still carries measurable cardiovascular risks - even now.

Researchers found higher post-COVID rates of
hypertension
arrhythmias
myocarditis
venous thrombosis
and even cardiomyopathy or heart failure
- compared to non-infected peers, regardless of initial severity.

So
Delta left stronger, more obvious sequelae.
Omicron looks milder acutely, but it’s not biologically neutral.
In a fraction of children, the infection still leaves a detectable vascular and immune imprint.

In kids, COVID rarely looks dramatic - but it doesn’t vanish without a trace.
The virus leaves subtle, measurable effects on vessels, the heart, and immunity.
Mild ≠ harmless.
Preventing infection is important.

Public health failed to recognize that not hospitalized ≠ unaffected.
Kids deserve protection not only from death, but from the silent biology that shapes their future health. @szupraha @ZdravkoOnline @adamvojtech86

Even when symptoms fade, biology doesn’t always reset.
Endothelial scars, immune shifts, and metabolic traces can persist - shaping long-term health in ways we’re only beginning to map.

Sampri at 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. Child & Adolescent Health 2025. thelancet.com/journals/lanch…

Zhang at al., Cardiovascular post-acute sequelae of SARS-CoV-2 in children and adolescents: cohort study using electronic health records. Nature Communications 2025. nature.com/articles/s4146…