CHICAGO (AP) — Chicago experienced a significant spike in COVID-19 cases in the last week, triggering fresh concerns Tuesday from the city’s top health officials.

The average number of confirmed daily cases in the nation’s third-largest city was 350 Tuesday, up 23% from 285 the week before, according to city data.

Department of Public Health Commissioner Dr. Allison Arwady said the biggest driver behind the increase was young adults, led by those ages 18 to 29, and a similar uptick preceded an October surge.

“We are worried about this,” Arwady said during an online event.

However, she said increasing vaccinations would hopefully prevent another surge.

Starting Monday, Chicago is expanding COVID-19 vaccine eligibility to people with health conditions and more categories of workers. Illinois expanded eligibility last month but Chicago and surrounded areas held off because of limited vaccine supplies.

Meanwhile, the city’s health department announced it was ending its partnership with a vaccine distributor that “knowingly misallocated” more than 6,000 doses. Innovative Express Care had a contract to vaccinate Chicago Public Schools employees. But city officials said non-CPS employees were vaccinated and vaccines set aside as second doses were used as first doses.

Arwady said the good news is Chicago’s COVID-19 infection rates by race now more closely match the population. Throughout the pandemic, case rates among Black and Latino Chicagoans have been disproportionately high.

By SOPHIA TAREEN