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We wish to thank Erren and Morfeld for their comment, which illustrates how SMR can be a useful measure of the impact of epidemic diseases (1).

The aim of our article was to describe strengths and limitations of epidemiological indicators used during early phases of an epidemic to characterize the impact of the infection and the disease on a population (2). We discussed that measures of mortality, such as SMR, can be valuable in later phases of the epidemic, while their interpretation is difficult in early phases, especially when comparing different territories.

However, SMR, like the other indicators discussed in our article, also present some limitations:

  • The choice of the reference period for the baseline is crucial, but somehow arbitrary: different reference periods might result in different numbers of expected-cases.
  • The excess in mortality due to the direct effect of COVID-19 might be overestimated. Psychosocial factors, official regulations or lack in healthcare capacities might hinder access to healthcare for individuals not affected by COVID-19 with an impact on patients’ survival probability (indirect effect).
  • Differences in mortality patterns before the spread of a virus need to be considered. For example in Italy—before the COVID-19 epidemic, after a warmer 2019 winter season and a less intense seasonal influenza wave—the observed mortality rates were lower than expected, thus potentially inflating the pool of individuals with high susceptibility to fatal COVID-19 disease courses (3).

Despite these methodological challenges, SMRs are and will be a useful instrument for the impact assessment in later phases of an epidemic (4).

DOI: 10.3238/arztebl.2020.0754b

Dr. rer. physiol. Emilio Gianicolo, Nicola Riccetti,
Prof. Dr. rer. nat. Maria Blettner
Institute for Medical Biostatistics
Epidemiology, and Informatics (IMBEI),
Mainz University Medical Center,Mainz, Germany
emilio.gianicolo@uni-mainz.de

Prof. Dr. med. André Karch, MSc
Institute for Epidemiology and Social Medicine,
Faculty of Medicine,
Westfälische Wilhelms University of Münster, Germany

Conflict of interest statement
The authors of both contributions declare that no conflict of interest exists.

1.
Erren TC, Morfeld P: COVID-19-Mortalität: Mit viel Sicht fliegen. Dtsch Arztebl 2020; 117: A-1010 VOLLTEXT
2.
Gianicolo E, Riccetti N, Blettner M, Karch A: Epidemiological measures in the context of the COVID-19 pandemic. Dtsch Arztebl Int 2020; 117: 336–42 VOLLTEXT
3.
Davoli, de‘ Donato, De Sario et al.: Andamento della mortalita giornaliera (SiSMG) nelle citta italiane in relazione all’epidemiadi Covid-19. www.deplazio.net/images/stories/SISMG/SISMG_COVID19.pdf (last accessed on 23 July 2020).
4.
Michelozzi P, de‘Donato F, Scortichini M, et al.: Mortality impacts of the coronavirus disease (COVID-19) outbreak by sex and age: rapid mortality surveillance system, Italy, 1 February to 18 April 2020. Euro Surveill 2020; 25: 2000620 CrossRef MEDLINE PubMed Central
1.Erren TC, Morfeld P: COVID-19-Mortalität: Mit viel Sicht fliegen. Dtsch Arztebl 2020; 117: A-1010 VOLLTEXT
2.Gianicolo E, Riccetti N, Blettner M, Karch A: Epidemiological measures in the context of the COVID-19 pandemic. Dtsch Arztebl Int 2020; 117: 336–42 VOLLTEXT
3.Davoli, de‘ Donato, De Sario et al.: Andamento della mortalita giornaliera (SiSMG) nelle citta italiane in relazione all’epidemiadi Covid-19. www.deplazio.net/images/stories/SISMG/SISMG_COVID19.pdf (last accessed on 23 July 2020).
4.Michelozzi P, de‘Donato F, Scortichini M, et al.: Mortality impacts of the coronavirus disease (COVID-19) outbreak by sex and age: rapid mortality surveillance system, Italy, 1 February to 18 April 2020. Euro Surveill 2020; 25: 2000620 CrossRef MEDLINE PubMed Central

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