Direct and indirect effects of the COVID-19 pandemic on mortality in Switzerland

Abstract

The direct and indirect impact of the COVID-19 pandemic on population-level mortality is of concern to public health but challenging to quantify. Using data for 2011-2019, we applied Bayesian models to predict the expected number of deaths in Switzerland and compared them with laboratory-confirmed COVID-19 deaths from February 2020 to April 2022 (study period). We estimated that COVID-19-related mortality was underestimated by a factor of 0.72 (95% credible interval [CrI]: 0.46-0.78). After accounting for COVID-19 deaths, the observed mortality was -4% (95% CrI: -8 to 0) lower than expected. The deficit in mortality was concentrated in age groups 40-59 (-12%, 95%CrI: -19 to -5) and 60-69 (-8%, 95%CrI: -15 to -2). Although COVID-19 control measures may have negative effects, after subtracting COVID-19 deaths, there were fewer deaths in Switzerland during the pandemic than expected, suggesting that any negative effects of control measures were offset by the positive effects. These results have important implications for the ongoing debate about the appropriateness of COVID-19 control measures.

Fig. 1. Observed and expected number of deaths, relative excess mortality, and the Oxford stringency index.

A Observed and expected number of weekly deaths by age group in Switzerland from February 2020 to April 2022. Model-predicted expected deaths are shown with a median and 95% credibility interval. Numbers at the top indicate epidemic phases 1–7. B Estimated relative excess mortality by seven epidemic phases from February 2020 to April 2022 and five age groups. Medians with 95% credible intervals (error bars) are shown. See Online Supplementary Table S3 for the size of each group. C Timeline of the Oxford stringency index in Switzerland. n = 588,739 during January 2011 and December 2019 and n = 156,193 observed all-cause deaths during February 2020 and April 2022 were used to derive the above statistics.

Fig. 2. Excess all-cause and laboratory-confirmed COVID-19-related deaths.

Weekly counts of excess all-cause deaths (95% credibility intervals) and of laboratory-confirmed COVID-19-related deaths between February 24, 2020 and April 3, 2022 in Switzerland by five age groups. Numbers at the top indicate epidemic phases 1–7.

Fig. 3. Direct (β₁) and indirect (β₂) effects of the COVID−19 pandemic and all-cause mortality by age and epidemic phase.

A Association between weekly laboratory-confirmed COVID-19-related deaths and absolute excess mortality by age group. The black line shows the slope of association corresponding to a 1 to 1 relation. The red lines show the association estimated with the model (corresponding to the ${\beta }_1$ coefficients shown in panel (B), the full line represents the point estimate and the dashed lines the lower and upper bounds of the 95% credible interval). B Estimates of ${\beta }_1$, the additional number of deaths to be observed for each unit increase in laboratory-confirmed deaths, after adjusting for the expected number of all-causes deaths given historical trends. The error bars denote the 95% Credible Intervals. See Online Supplementary Table S3 for the size of each group. C Estimates of ${\beta }_2$, the additional number of deaths to be observed for each unit increase in the expected number of all-cause deaths, after adjusting for the direct effect of SARS-CoV−2 infections. The error bars denote the 95% credible intervals. See Online Supplementary Table S3 for the size of each group. n = 156,193 number of observed all-cause deaths were used to derive the above statistics.