COVID-19 hospitalizations among those in their 30s have reached a new record, U.S. data shows, with doctors attributing the rise to the Delta variant’s grip over the unvaccinated.

According to the U.S. Centers for Disease Control, the rate among those between the ages 30 and 39 entering the hospital is 2.5 among 100,000 people as of Wednesday, up from a January record of 2 per 100,000. Doctors pointed to the increased transmissibility of the Delta variant, which has hit an age group once thought largely impervious to hospitalization. That risk is also amplified by increased socialization, providing more avenues for those unvaccinated in their 30s to catch the virus. “It loves social mobility,” Dr. James Fiorica, chief medical officer of a hospital in Sarasota, Florida, told The Wall Street Journal. “An unvaccinated 30-year-old can be a perfect carrier.”

It’s led some doctors in Arkansas to monitor younger patients for possible organ failure. “This age group pretty much went unscathed,” Nikhil Meena, the medical director of the University of Arkansas Medical Center’s ICU, said. “They’re all out there doing their thing and getting infected and getting sick enough to be in this hospital.”