An unvaccinated health worker triggered a Covid-19 outbreak in a Kentucky nursing home where the vast majority of residents had been vaccinated, leading to dozens of infections, including 22 cases among residents and workers already fully vaccinated, a new study reported Wednesday.
Most of those infected with the coronavirus despite vaccination did not develop symptoms or had to be hospitalized, but one vaccinated person, living in the nursing home, died, according to the study released by the Centers for Disease Control and Prevention .
In total, 26 residents of the facility were infected, including 18 who had been vaccinated, and 20 medical personnel were infected, including four who had been vaccinated. Two unvaccinated residents also died.
The report underscores the importance of vaccinating both nursing home residents and health professionals entering and exiting the sites, the authors said. While 90 percent of the 83 residents of the Kentucky nursing home had been vaccinated, only half of the 116 workers had been vaccinated when the outbreak was diagnosed in March this year.
The study, released in conjunction with a study involving nursing homes in Chicago, underscored the importance of enforcing measures such as the use of protective clothing, infection control protocols and routine testing, regardless of vaccination level. The emergence of virus variants has also raised concern.
According to the authors, a team of researchers from the CDC and the Kentucky Public Health Department, vaccine resistance is high among nursing home staff across the country, and the low acceptance rate of vaccination increases the likelihood of outbreaks in institutions.
“To protect skilled nursing facility residents, it is imperative that health care providers, as well as skilled nursing facility residents, are vaccinated,” the authors of the Kentucky study wrote.
The outbreak involved a variant of the virus with multiple mutations in the spike protein, the kind that makes the vaccines less effective. Vaccinated residents and health workers at the Kentucky facility were less likely to be infected than those who were not vaccinated, and they were much less likely to develop symptoms. The study estimated that the vaccine, identified as Pfizer-BioNTech, showed an effectiveness of 66 percent for residents and 75.9 percent for workers, and was 86 percent to 87 percent effective at protecting against symptomatic disease.
In the Kentucky outbreak, the virus variant is not listed among the CDCs considered to be of concern or interesting variants. However, the study authors note, the variant has several important mutations: D614G, which shows evidence of increased transmissibility; E484K in the receptor binding domain of the spike protein, also seen in B.1.351, the variant first recognized in South Africa, and P.1. from Brazil; and W152L, which could reduce the effectiveness of neutralizing antibodies.
In Chicago, meanwhile, routine screening of nursing home residents and staff members in February identified 627 coronavirus infections in 78 skilled nursing facilities across the city, but only 22 were found in individuals already fully vaccinated. Two-thirds of the cases in the vaccinated individuals were asymptomatic, the report found, but two residents were hospitalized and one died.
The Chicago study authors said their findings show that nursing homes should continue to follow recommended infection control practices, such as isolation and quarantine, use of personal protective equipment, and routine testing, regardless of vaccination status.
They also stressed the importance of “maintaining high vaccination coverage among residents and staff” to “reduce the potential for intra-facility transmission and exposure among individuals who may not have achieved protective immunity after vaccination.”