It's tempting to think that once your children have had COVID, they're protected from another round of serious illness. But this assumption is risky.

A recent study has found that children and teenagers who are reinfected with the SARS-CoV-2 virus are twice as likely to develop long COVID compared to being infected only once.

Catching COVID again may make children more vulnerable to lingering and serious health problems.

The results, based on the electronic health records of more than 465,000 young people under the age of 21 who were treated at 40 children's hospitals across the United States and who had had either one or two COVID infections between January 2022 and October 2023, were striking.

The rate of long COVID among children and adolescents who were reinfected was nearly 1,900 per million after two infections. By comparison, the rate of long COVID was less than half that — 904 per million — among those kids who had had just one infection.

In other words, the risk of developing long COVID doubles after infection.

It's important to understand that long COVID isn't a single condition. Rather, it's a constellation of symptoms, from fatigue and brain fog to heart and gastrointestinal problems, that can disrupt a life.

In this study, children reinfected with COVID faced significantly higher odds of severe complications. For instance, children infected with COVID a second time were:

  • Over three and a half times more likely to develop myocarditis (inflammation of the heart muscle), a potentially life-threatening condition.
  • Nearly three times more likely to experience changes in taste and smell.
  • Over two times more likely to develop blood clots.
  • Nearly twice as likely to suffer from heart disease or kidney damage.

Many of these children had no prior chronic health conditions.

As one of the study's senior authors, Yong Chen, Professor of Biostatistics and Director of the Penn Computing, Inference and Learning Lab at the Perelman School of Medicine, University of Pennsylvania, told the New York Times: “Your body has a memory system and is really going to be hurt from recurrent infection.”

Kids' risk of developing long COVID doubles with a second infection.

“The results of this study further support one of the strongest reasons I give patients, families and physicians about getting vaccinated,” Ravi Jhaveri, Head of Pediatric Infectious Diseases at Ann & Robert H. Lurie Children's Hospital of Chicago, Professor of Pediatrics at Northwestern University Feinberg School of Medicine and the study's co-author, said in a media release. “More vaccines should lead to fewer infections, which should lead to less long COVID.”

About three-quarters of children in the study were unvaccinated, in part because vaccines weren't initially available to younger age groups. While the study didn't specifically measure how vaccines affect long COVID, previous research has shown that vaccination significantly lowers risk — both by preventing severe illness and by reducing the odds of developing long-term complications.

The research puts to rest the notion that COVID becomes “milder” with reinfection. On the contrary, the evidence shows that catching COVID again may make children more vulnerable to lingering and serious health problems.

Misinformation has circulated the idea that healthy kids don't need COVID shots, but the evidence says otherwise. Vaccination continues to be the most effective tool to reduce infections and lower the risks of long COVID. Simply put: Getting COVID once does not grant immunity or protect your child from future infections.

The study is published in The Lancet Infectious Diseases.