Global epidemiology and socio-economic development correlates of the reproductive ratio of COVID-19

Abstract

Background: The most commonly cited argument for imposing or lifting various restrictions in the context of the coronavirus disease 2019 (COVID-19) pandemic is an assumed impact on the reproductive ratio of the pathogen. It has furthermore been suggested that less-developed countries are particularly affected by this pandemic. Empirical evidence for this is lacking.

Methods: Based on a dataset covering 170 countries, patterns of empirical 7-d reproductive ratios during the first months of the COVID-19 pandemic were analysed. Time trends and associations with socio-economic development indicators, such as gross domestic product per capita, physicians per population, extreme poverty prevalence and maternal mortality ratio, were analysed in mixed linear regression models using log-transformed reproductive ratios as the dependent variable.

Results: Reproductive ratios during the early phase of a pandemic exhibited high fluctuations and overall strong declines. Stable estimates were observed only several weeks into the pandemic, with a median reproductive ratio of 0.96 (interquartile range 0.72-1.34) 6 weeks into the analysis period. Unfavourable socio-economic indicators showed consistent associations with higher reproductive ratios, which were elevated by a factor of 1.29 (95% confidence interval 1.15 to 1.46), for example, in the countries in the highest compared with the lowest tertile of extreme poverty prevalence.

Conclusions: The COVID-19 pandemic has allowed for the first time description of the global patterns of reproductive ratios of a novel pathogen during pandemic spread. The present study reports the first quantitative empirical evidence that COVID-19 net transmissibility remains less controlled in socio-economically disadvantaged countries, even months into the pandemic. This needs to be addressed by the global scientific community as well as international politics.

Keywords: SARS-CoV-2; ecological study; health disparities.

Figure 1.

Distribution of the empirical COVID-19 reproductive ratio over time in 140 countries fulfilling criteria for robust analysis. The upper panel shows the data of each country connected by lines, whereas the bottom panel shows violin plots of the reproductive ratios at selected time points.