An unvaccinated health care worker sparked a Covid-19 outbreak in a Kentucky nursing home where the vast majority of residents had been vaccinated. This resulted in dozens of infections, including 22 cases in residents and staff who were already fully vaccinated. This is a new study reported Wednesday.
Most people who were infected with the coronavirus despite being vaccinated did not develop symptoms or had to be hospitalized. A vaccinated person who lived in the nursing home died, according to the study published by the Centers for Disease Control and Prevention.
A total of 26 residents of the facility were infected, including 18 vaccinated, and 20 healthcare workers, including four vaccinated. Two unvaccinated residents also died.
The report underscores the importance of vaccination for both nursing home residents and health care workers entering and leaving the sites, the authors say. While 90 percent of the 83 Kentucky nursing home residents were vaccinated, only half of the 116 employees had been vaccinated when the outbreak was detected in March this year.
The study, which was published along with a study involving nursing homes in Chicago, highlighted the importance of maintaining measures such as the use of protective equipment, infection control protocols, and routine testing regardless of the level of vaccination rates. The rise in virus variants has also raised concerns.
Resistance to vaccines has been high among nursing home workers across the country, and low vaccine acceptance rates increase the likelihood of outbreaks in facilities, according to the authors, a team of investigators from the C.D.C. and the Kentucky Health Department.
"To protect skilled care residents, it is imperative that both healthcare providers and qualified care residents are vaccinated," the authors of the Kentucky study write.
The outbreak affected a variant of the virus that has multiple mutations in the spike protein that make the vaccines less effective. Vaccinated residents and health care workers at the Kentucky facility were less infected than those who had not been vaccinated and were far less likely to develop symptoms. The study estimated that the vaccine identified as Pfizer-BioNTech showed 66 percent effectiveness for residents and 75.9 percent for employees, and was 86 to 87 percent effective at protecting against symptomatic disease.
In the Kentucky outbreak, the virus variant was not on the list of C.D.C. However, the study's authors note that the variant has several important mutations: D614G, which shows evidence of increased transferability; E484K in the receptor binding domain of the spike protein, which can also be 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 in February, routine exams of nursing home residents and staff found 627 coronavirus infections in 78 qualified nursing homes across the city, but only 22 were found in those who were already fully vaccinated. According to the report, two-thirds of the cases in those vaccinated were asymptomatic, but two residents were hospitalized and one died.
The Chicago study authors said their results show that regardless of vaccination status, nursing homes should continue to follow recommended infection control methods such as isolation and quarantine, use of personal protective equipment, and routine testing.
They also stressed the importance of "maintaining high levels of vaccination among residents and staff" in order to "reduce the chance of transmission within facilities and the exposure of people who may not have achieved protective immunity after vaccination".