A separate American Association of Retired Persons analysis, released last week, showed that only one in five of the nation’s more than 15,000 nursing homes were able to hit a goal, set by two industry trade groups, of vaccinating 75% of their staff by the end of June.

While cases in nursing homes have recently slowed, and most of the new COVID-19 infections are among younger people, some experts still worry of a return to darker days.

The CDC recently launched an investigation into deaths of residents at several western Colorado senior facilities possibly linked to unvaccinated staff, the Associated Press reported Wednesday.

“We need to sound the alarm,” said Susan Reinhard, senior vice president of AARP and director of its Public Policy Institute. “Nursing homes were devastated by COVID-19, and many residents remain highly vulnerable to the virus.”