A COVID-19 outbreak in a Kentucky nursing home was caused by a single unvaccinated worker, according to a new study from Centers for Disease Control and Prevention, but the residents and workers who were vaccinated were much better protected.
The outbreak was linked to dozens of infections in both workers and residents, including 22 residents and workers who had already been vaccinated. The virus was introduced by a single employee who was unvaccinated and symptomatic.
However, the number of attacks was three to four times higher among unvaccinated residents and workers than among those vaccinated, and the vaccinated staff and residents were significantly less likely to have symptoms or hospitalization.
During the outbreak, 46 COVID-19 cases were identified, the CDC said, including cases in 26 residents, where 18 were fully vaccinated and 20 medical personnel, where four were vaccinated.
A vaccinated resident, who had become infected 300 days earlier, became infected again during the outbreak and died. Two unvaccinated residents also died.
The low rate of breakthrough infections and the fact that most breakthrough infections were asymptomatic underline the importance of vaccination of nursing home residents and staff.
The coronavirus is most likely introduced to a nursing home through an infected staff member who regularly enters and leaves the facility. At the researched CDC nursing home in Kentucky, 90 percent of the 83 residents were vaccinated, but only half of the 116 staff were at the time of the March outbreak.
Low vaccination acceptance among nursing home workers is a nationwide challenge and could increase the likelihood of COVID-19 introduction and transmission within an institution, the CDC said.
Vaccination of workers and residents “is critical to reduce the risk of the introduction, transmission and serious consequences of SARS-CoV-2” in nursing facilities, the CDC said.
The outbreak involved the R.1 variant of the virus, which the CDC does not list as a variant of concern, but still contains multiple mutations in the spike protein that could make vaccines less effective.
The Pfizer BioNTech vaccine showed an effectiveness of 66 percent for residents against infection and 75.9 percent for workers.
The CDC acknowledged that both figures are lower than those reported from Israel’s national vaccination program. This may be due to reduced protection against the R.1 variant, but also a small sample size and the higher risk of exposure associated with an outbreak in a common environment
Still, the CDC said vaccinated residents and staff were 87 percent less likely to have symptomatic COVID-19 compared to those who were not vaccinated.
Meanwhile, a separate study published simultaneously to nursing homes in the Chicago area found that among 627 people with COVID-19 infections in 75 nursing homes, only 22 infections were found in people who had been vaccinated and that no facility-related secondary transmission occurred.
Nearly two thirds of those breakthrough infections were asymptomatic. Still, two residents were hospitalized because of COVID-19 and one died.
CDC said the Chicago study shows that nursing homes should still follow recommended infection and control practices and promote high vaccination coverage among residents and staff.