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[Preprint]. 2022 Jan 11:2022.01.09.22268984.
doi: 10.1101/2022.01.09.22268984.

Household secondary attack rates of SARS-CoV-2 by variant and vaccination status: an updated systematic review and meta-analysis

Zachary J Madewell  1 , Yang Yang  1 , Ira M Longini Jr  1 , M Elizabeth Halloran  2 , Natalie E Dean  1
Affiliations

Household secondary attack rates of SARS-CoV-2 by variant and vaccination status: an updated systematic review and meta-analysis

Zachary J Madewell et al. medRxiv. .

Update in

Abstract

We previously reported a household secondary attack rate (SAR) for SARS-CoV-2 of 18.9% through June 17, 2021. To examine how emerging variants and increased vaccination have affected transmission rates, we searched PubMed from June 18, 2021, through January 7, 2022. Meta-analyses used generalized linear mixed models to obtain SAR estimates and 95%CI, disaggregated by several covariates. SARs were used to estimate vaccine effectiveness based on the transmission probability for susceptibility ( VE S,p ), infectiousness ( VE I,p ), and total vaccine effectiveness ( VE T,p ). Household SAR for 27 studies with midpoints in 2021 was 35.8% (95%CI, 30.6%-41.3%), compared to 15.7% (95%CI, 13.3%-18.4%) for 62 studies with midpoints through April 2020. Household SARs were 38.0% (95%CI, 36.0%-40.0%), 30.8% (95%CI, 23.5%-39.3%), and 22.5% (95%CI, 18.6%-26.8%) for Alpha, Delta, and Beta, respectively. VE I,p , VE S,p , and VE T,p were 56.6% (95%CI, 28.7%-73.6%), 70.3% (95%CI, 59.3%-78.4%), and 86.8% (95%CI, 76.7%-92.5%) for full vaccination, and 27.5% (95%CI, -6.4%-50.7%), 43.9% (95%CI, 21.8%-59.7%), and 59.9% (95%CI, 34.4%-75.5%) for partial vaccination, respectively. Household contacts exposed to Alpha or Delta are at increased risk of infection compared to the original wild-type strain. Vaccination reduced susceptibility to infection and transmission to others.

Summary: Household secondary attack rates (SARs) were higher for Alpha and Delta variants than previous estimates. SARs were higher to unvaccinated contacts than to partially or fully vaccinated contacts and were higher from unvaccinated index cases than from fully vaccinated index cases.

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Figures

Figure 1.
Figure 1.. Household secondary attack rates over time (by study midpoint), 126 studies (unvaccinated index cases, unvaccinated contacts).
Restricted to laboratory-confirmed results only. The blue line is a loess smoothing line and bands are 95% confidence intervals. Bicolored points represent studies with 2 predominant variants.
Figure 2.
Figure 2.
Household secondary attack rates for Alpha (B.1.1.7), Delta (B.1.617.2), and Beta (B.1.351) variants.
Figure 3.
Figure 3.. Household secondary attack rates by index case vaccination status.
All contacts are included regardless of vaccination status. *For Harris et al., most of the vaccinated index cases (93%) had received only the first dose of vaccine and secondary attack rates were not disaggregated by dose.
Figure 4.
Figure 4.. Household secondary attack rates by contact vaccination status.
All index cases are included regardless of vaccination status.
See this image and copyright information in PMC

References

    1. Madewell ZJ, Yang Y, Longini IM Jr., Halloran ME, Dean NE. Factors Associated With Household Transmission of SARS-CoV-2: An Updated Systematic Review and Meta-analysis. JAMA Netw Open 2021; 4(8): e2122240. - PMC - PubMed
    1. Centers for Disease Control and Prevention. Global Variants Report. Available at: https://covid.cdc.gov/covid-data-tracker/#global-variant-report-map.
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    1. Shapiro J, Dean NE, Madewell ZJ, Yang Y, Halloran ME, Longini I. Efficacy Estimates for Various COVID-19 Vaccines: What we Know from the Literature and Reports. medRxiv 2021: 2021.05.20.21257461.
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