Children and teenagers are twice as likely to develop long Covid after a second coronavirus infection as after an initial infection, a large new study has found.
The study, of nearly a half-million people under 21, published Tuesday in Lancet Infectious Diseases, provides evidence that Covid reinfections can increase the risk of long-term health consequences and contradicts the idea that being infected a second time might lead to a milder outcome, medical experts said.
Dr. Laura Malone, director of the Pediatric Post-Covid-19 Rehabilitation Clinic at Kennedy Krieger Institute in Baltimore, who was not involved in the study, said the findings echo the experience of patients in her clinic.
“Just because you got through your first infection and didn’t develop long Covid, it’s not that you are completely out of the woods,” she said.
The study, conducted as part of the National Institutes of Health’s RECOVER Initiative, examined electronic medical records for about 465,000 young people at 40 children’s hospitals in the United States. They had either a first or a second coronavirus infection between Jan. 1, 2022, and Oct. 13, 2023. The study focused on the Omicron wave, but researchers said the conclusions are most likely relevant to more recent variants.
The authors counted how many young people received a specific diagnostic code for long Covid that was added to the International Classification of Diseases in October 2021. The rate over a six-month period showed that 1,884 per million young people developed long Covid after two infections, twice the rate of 904 per million for young people with one infection.
“Reinfection really increases the risk,” said Yong Chen, the study’s senior author, a professor of biostatistics at the University of Pennsylvania and director of the Penn Computing, Inference and Learning Lab. “Your body really has a memory system and is really going to be hurt from recurrent infection.”
The study also found that tens of thousands of young people who did not receive a long Covid diagnosis were treated for conditions that can be symptoms of long Covid, including respiratory problems and abdominal pain. As a result, Dr. Chen said, the diagnostic code most likely captured only “a subset of the long Covid.”
Studies of adults have found that they also face greater risk of developing long Covid after being infected with the virus more than once.