Study population and setting
While the individual level effectiveness of the Pfizer-BioNTech vaccine for SARS-CoV-2 is well-established, few studies have addressed its ability to reduce transmission in a population. This study describes the impact of the Pfizer-BioNTech vaccine on household transmission in Israel between June 15, 2020, and March 24, 2021. Data were collected from the Maccabi Healthcare Services database, which covers a representative sample of about 1/4 of the Israeli population. The study population included households with at least one SARS-CoV-2 infected individual and at least two household members (253,564 individuals from 65,624 households). Researchers used two different time-to-event models to calculate estimates of vaccine effectiveness against vaccine breakthrough infection (given known exposure) and transmission.
Summary of Main Findings
Using a mechanistic model for household transmission, researchers estimated that vaccination (two doses of Pfizer-BioNTech) was 80.5% (95% CI: 78.9-82.1) effective against breakthrough infection (given exposure) and 41.3% (95% CI: 9.5-73.0) effective at reducing infectiousness in cases of vaccine breakthrough. Combining these two reductions of risk, this model estimated that vaccination led to an 88.5% (95% CI: 82.3-94.8) reduction in overall transmission risk for this population. An alternative model, based on an infection-hazard approach, estimated a 92.3% (95% CI: 90.2-94.5) reduction in hazard of infection, given exposure of a vaccinated household member to an infected, unvaccinated household member, as well as a 78.6% (95% CI: 74.5-82.7) reduction in hazard of infection, given exposure of an unvaccinated household member to an infected, vaccinated household member. While these models approach vaccine-associated risk reduction from different perspectives and are not directly comparable, they both demonstrate clear associations between vaccination and reductions in breakthrough infection and transmission.
Study data were collected from a well-maintained, state-sponsored database that covers a large, representative sample of the Israeli population. Models were adjusted for age, time-varied risk (based on community-level outbreak levels), and vaccination status of all household members. Two distinct models with different approaches provided similar conclusions regarding the impact of vaccination on SARS-CoV-2 breakthrough infection and transmission.
Time of infection and duration of infectiousness were estimated using data augmentation. If individuals included in this dataset were infected but not tested (due to asymptomatic or mild infection), they would have been misclassified as uninfected. Analysis was restricted by household size and the requirement that one individual test positive for SARS-CoV-2. This study was completed prior to the rise of the Delta variant and does not capture its likely significant impact on vaccine effectiveness against breakthrough infection and transmission.
This large-scale study demonstrated that widespread vaccination with the Pfizer-BioNTech vaccine led to reduced SARS-CoV-2 transmission in households in Israel between June 2020 and March 2021.
This review was posted on: 9 August 2021