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

  1. Maylis Layan
  2. Mayan Gilboa
  3. Tal Gonen
  4. Miki Goldenfeld
  5. Lilac Meltzer
  6. Alessio Andronico
  7. Nathanaël Hozé
  8. Simon Cauchemez
  9. Gili Regev-Yochay

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Abstract

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.

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  1. Version published to 10.1093/aje/kwac042
  2. ScreenIT

    SciScore for 10.1101/2021.07.12.21260377: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsConsent: Those who agreed and gave their consent, answered a telephone interview.
    IRB: Ethics: The study was approved by the Sheba Medical Center IRB committee (approval #8130-21).
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study has several limitations. First, household studies such as ours may be affected by multiple sources of bias. On the one hand, we may overestimate the SAR if we are more likely to detect household with multiple cases. On the other hand, we might underestimate it if some asymptomatic, or pauci-symptomatic cases are missed by surveillance. Second, we estimated an important reduction of infectivity in vaccinated cases with 2 doses compared to unvaccinated cases as previously shown.10,11 However, this is associated with important uncertainty due to the small number of cases (15 vaccinated index cases, and 19 vaccinated secondary cases). Thus, more data are needed to reduce the size of credible intervals. Third, we assumed an all-or-nothing effect of the vaccine that started seven days after the second dose (or 15 days after the first dose in our sensitivity analysis). In practice, the effect of the vaccine is likely to be progressive, which might push down estimates of efficacy since individuals with early partial protection would be considered as unvaccinated. However, excluding households with the early-vaccinated index cases did not impact our estimates (Supplementary Figure 2). The limited number of households does not make it possible to dissociate early vs full protection conferred by the vaccine nor to investigate the infectivity of children relative to adults/teenagers. To conclude, vaccination with two doses substantially reduces the risk of transmission and the ...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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  3. Version published to 10.1101/2021.07.12.21260377v1 on medRxiv