Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky urged Americans aged six months and older to get their flu shots as health officials prepare for a potentially “severe” flu season.

The CDC is preparing for the return of the flu after last year saw a “near absence” of it, Walensky said as she advocated for the vaccine during a National Foundation for Infectious Disease (NFID) news conference on Thursday.

The low levels of flu last year, likely due to COVID-19 prevention measures, could contribute to a worse season this year, public health experts have said.

“Because of so little disease last year, population immunity is likely lower, putting us all at increased risk for disease this year especially among those most vulnerable, including our children,” Walensky said.

“This is why it is doubly important this year that we build up community immunity with vaccination as we head into the fall and winter,” she added.

Current status: The U.S. is on track to match last season when 52 percent of those older than six months for the flu shot, she said.