Infants under one are proportionally more likely to be hospitalized with the omicron variant of the coronavirus than older children but they did not become particularly sick, British researchers said.

Of children hospitalized with COVID-19 in the last four weeks, 42 percent were under one, compared with around 30 percent in previous waves, the early data showed.

Presenting the data, Russell Viner, professor of child and adolescent health at University College London, told reporters the trend was likely in part because omicron symptoms might resemble the sort of respiratory conditions that would encourage parents to take babies to hospital as a precaution.

“These are not particularly sick infants. In fact, they’re coming in for short periods of time,” study author Calum Semple, professor in child health and outbreak Medicine at, the University of Liverpool, added, saying the proportion requiring oxygen was falling.

omicron has spread rapidly in Britain and fueled a spike in cases to record highs, though the variant is less severe than previous ones, and high vaccination levels among adults have also helped to limit the rise in hospitalizations. Children are less vulnerable than older adults to COVID-19.

The study was shared with government advisers, who published it on Friday.