Household size can explain 40% of the variance in cumulative COVID-19 incidence across Europe

TL;DR

This study quantifies how household size significantly influences COVID-19 spread across Europe, showing larger households contribute more to transmission and require stricter interventions for containment.

Contribution

The paper introduces a method to separate within- and out-household transmission, quantifying household size's role in epidemic variability across countries.

Findings

Household size explains 41% of COVID-19 incidence variability across 34 European countries.

Larger households increase the effective transmission boost factor.

Countries with bigger households need stricter measures for effective containment.

Abstract

Household size impacts the spread of respiratory infectious diseases: Larger households tend to boost transmission by acquiring external infections more frequently and subsequently transmitting them back into the community. Furthermore, mandatory interventions primarily modulate contagion between households rather than within them. We developed an approach to quantify the role of household size in epidemics by separating within-household from out-household transmission, and found that household size explains 41% of the variability in cumulative COVID-19 incidence across 34 European countries (95% confidence interval: [15%, 46%]). The contribution of households to the overall dynamics can be quantified by a boost factor that increases with the effective household size, implying that countries with larger households require more stringent interventions to achieve the same levels of containment. This suggests that households constitute a structural (dis-)advantage that must be considered when designing and evaluating mitigation strategies.