In Washington state, half of new daily infections in early May were occurring in people under 40, a dramatic increase from eight weeks earlier, when older age groups made up more than two-thirds of the patients who tested positive, according to a new report. Based on public data from the Washington Department of Health, the analysis noted that cases in Washington state peaked on March 22, then declined for a few weeks, and then sustained a plateau with an average of approximately 200 cases per day since.

“Watch what’s happening before and after the peak,” said lead author Dr. Judith Malmgren, an epidemiologist and affiliate assistant professor at the University of Washington’s school of public health. “The disease didn’t change, but the people who were infected changed.”

Malmgren said the analysis—published on the preprint site for health sciences research, medRxiv, and not yet peer-reviewed—found 39 percent of confirmed cases in the state were in the 20-39 age bracket, and another 11 percent were in those 19 or younger. Though otherwise healthy young people are less likely to suffer serious illness from the virus than those over the age of 65 or with comorbidities, the disease can cause lifelong health effects on all patients, and recent reports of a life-threatening inflammatory syndrome in children has raised significant concerns across the country.