Transmission of B.1.617.2 Delta Variant Between Vaccinated Healthcare Workers

Abstract Breakthrough infections with SARS-CoV-2 Delta variant have been reported in vaccine recipients and in individuals infected with previous variants. Studies of viral spread within hospital settings have highlighted the potential for transmission between patients and health care workers, and highlighted the benefits of high-grade respiratory protection for health care workers. However the extent to which vaccination is preventative of viral spread in health care settings is less well studies. We here analyse data from health care workers in two hospitals in India, constructing probable transmission networks from epidemiological and virus genome sequence data using a suite of computational approaches. A maximum likelihood reconstruction of transmission involving known cases of infection suggests a high probability that doubly vaccinated health care workers transmitted SARS-CoV-2 between each other, and highlights potential cases of virus transmission between individuals who had received two doses of vaccine. Our findings support the need for ongoing infection control measures even in highly vaccinated populations.