COVID-19: How to make between-country comparisons

Abstract

Background: Different countries have adopted different containment and testing strategies for SARS-CoV-2. The difference in testing makes it difficult to compare the effect of different containment strategies. This study proposes methods to allow a direct comparison and presents the results.

Design: Publicly available data on the numbers of reported COVID-19-related deaths between 01 January and 17 April 2020 were compared between countries.

Results: The numbers of cases or deaths per 100,000 inhabitants gave severely biased comparisons between countries. Only the number of deaths expressed as a percentage of the number of deaths on day 25 after the first reported COVID-19-related death allowed a direct comparison between countries. From this comparison clear differences were observed between countries, associated with the timing of the implementation of containment measures.

Conclusions: Comparisons between countries are only possible when simultaneously taking into account that the virus does not arrive in all countries simultaneously, absolute numbers are incomparable due to different population sizes, rates per 100,000 of the population are incomparable because not all countries are affected homogeneously, susceptibility to death by COVID-19 can differ between populations, and a death is only reported as a COVID-19-related death if the patient was diagnosed with SARS-CoV-2 infection. With the current methods, all these factors were accounted for and an unbiased direct comparison between countries was established. This comparison confirmed that early adoption of containment strategies is key in flattening the curve of the epidemic.

Keywords: COVID-19; Forecast; Mortality; Prevention.

Figure 1

Different measures to compare the COVID-19 epidemic between countries. Dates from different countries were synchronised with the date of the first reported COVID-19-related case (panels A and C) or death (panels B and D) as day 1. Height of the curves represents the cumulative number of reported cases (panel A) or deaths (panel B) per 100,000 inhabitants or the cumulative number of reported cases (panel C) or deaths (panel D) expressed as a percentage of the number of deaths on day 25 in that country. Panel A: Cumulative number of cases per 100,000 from 01 January to 17 April 2020. Panel B: Cumulative number of deaths per 100,00 from 01 January to 17 April 2020. Panel C: Cumulative number of cases as % on day 25 from 01 January to 17 April. Panel D: Cumulative number of deaths as % on day 25 from 01 January to 17 April.

Figure 2

Cumulative number of deaths as % on day 25 from 01 January to 17 April in China and South Korea (with a pre-emptive containment policy). Dates from different countries were synchronised with the date of the first reported COVID-19-related death as day 1. Height of the curves represents the cumulative number of reported COVID-19-related deaths in that country, expressed as a percentage of the number of deaths on day 25 in that country.

Figure 3

Cumulative number of deaths as % on day 25 from 01 January to 17 April in China and the USA (a country with late containment policy). Development of the epidemic in the United States of America compared with China. Dates from different countries were synchronised with the date of the first reported COVID-19-related death as day 1. Height of the curves represents the cumulative number of reported COVID-19-related deaths in that country, expressed as a percentage of the number of deaths on day 25 in that country.