CHICAGO (AP) — Illinois will help local health departments with additional staffing at mass vaccination sites, a move officials announced Monday as the state experienced its highest surge in COVID-19 cases during the entire coronavirus pandemic.

Gov. J.B. Pritzker said Illinois will add at least 100 people at local health department mass vaccination sites to meet growing demand. Staff will help prepare and administer vaccines, among other things. Starting next week, Illinois will also open its community-based testing sites six days a week.

The state, which surpassed 2 million infections earlier this month, is averaging 500 new daily hospital admissions for COVID-19. The number is double from roughly a month ago. Illinois Public Health Director Dr. Ngozi Ezike said the majority of those hospitalized are unvaccinated.

The world is seeing a COVID-19 surge fueled by the omicron variant, which is now the dominant version of COVID-19 in the U.S. As recently as the end of November, more than 99.5% of coronaviruses in the U.S. were delta, according to Centers for Disease Control and Prevention.

State health officials urged fresh caution at holiday gatherings.

“Every single event being held during this holiday season, will have one or two uninvited, unwanted guests: delta and or omicron. One or both could be there,” she said. “I’m not saying this to scare. I’m just saying this for people to be aware, but how we entertain that guest depends on us.”

She encouraged people wear masks at gatherings, limit exposure to crowds and to get booster vaccine doses to lower chances of severe illness.