Lagging vaccination rates among nursing home staff are being linked to a national increase in COVID-19 infections and deaths at senior facilities, and are at the center of a federal investigation in a hard-hit Colorado location where disease detectives found many workers were not inoculated. The investigation by the Centers for Disease Control and Prevention of facilities in the Grand Junction, Colorado, area raises concerns among public health doctors that successes in protecting vulnerable elders with vaccines could be in peril as the more aggressive delta variant spreads across the country. At one Colorado memory care facility, 16 fully vaccinated residents were infected and four died, according to a CDC slide provided to The Associated Press.