Impact of BNT162b2 Vaccination and Isolation on SARS-CoV-2 Transmission inIsraeli Households: An Observational Study

Several studies have characterized the effectiveness of vaccines against severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) infections. However, estimates of their impact on transmissibility remain limited.
Here, we evaluated the impact of isolation and vaccination (7 days after the second dose) on SARS-CoV-2
transmission within Israeli households. From December 2020 to April 2021, confirmed cases were identified
among health-care workers of the Sheba Medical Centre and their family members. Recruited households were
followed up with repeated PCR for at least 10 days after case confirmation. Data were analyzed using a data
augmentation Bayesian framework. A total of 210 households with 215 index cases were enrolled; 269 out of
667 (40%) susceptible household contacts developed a SARS-CoV-2 infection. Of those, 170 (63%) developed
symptoms. Compared with unvaccinated and unisolated adult/teenager (aged >12 years) contacts, vaccination
reduced the risk of infection among unisolated adult/teenager contacts (relative risk (RR) = 0.21, 95% credible
interval (CrI): 0.08, 0.44), and isolation reduced the risk of infection among unvaccinated adult/teenager (RR =
0.12, 95% CrI: 0.06, 0.21) and child contacts (RR=0.17, 95% CrI: 0.08, 0.32). Infectivity was reduced in vaccinated
cases (RR = 0.25, 95% CrI: 0.06, 0.77).Within households, vaccination reduces both the risk of infection and of
transmission if infected. When contacts were unvaccinated, isolation also led to important reductions in the risk
of transmission.
COVID-19; household; infectious disease transmission; physical distancing; SARS-CoV-2; vaccination; vaccine
effectiveness