Reply to Mattiuzzi and Lippi

To the editor—We would like to thank our colleagues Mattiuzzi and Lippi for confirming our conclusion [1] on Spanish flu being deadlier than coronavirus disease 2019 (COVID-19) by Italian figures [2]. Italy was the first European country hit by the COVID-19 pandemic and it was hit very hard. A reflection on death toll puts the events in a historical perspective. The conclusion of our Italian colleagues is based on a comparison of crude death rates. However, when comparing both pandemics, the difference of population structure should be taken into account. Therefore, we compared not only crude death rates, but also age-standardized death rates. As there is no gold standard in this case, we projected both the age-specific Spanish flu figures of 1918–1920 on the (average) 2020–2022 population, and conversely, we projected the age-specific COVID-19 figures of 2020–2022 on the (average) 1918–1920 population. The first projection resulted in a Spanish flu:COVID-19 ratio of 2.2, the second in a Spanish flu:COVID-19 ratio of 6.9. The outcome of the second projection is close to the estimate of our Italian colleagues.

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