Measuring the impact of COVID-19 in Italy and a global perspective

Introduction:
Different metrics have been used to monitor the impact of the COVID-19 pandemic, including the officially registered COVID-19 deaths. However, this metric has important limitations that can be partly addressed by considering total excess deaths. In this study, we compared trends in COVID-19 deaths in Italy with those observed globally and estimated the total number of excess deaths.

Material and methods:
We retrieved the number of COVID-19 deaths from the John Hopkins University and the daily number of deaths from any causes from the Italian National Institute of Statistics archives. We fitted an over-dispersed Poisson regression model on historical data to estimate the expected deaths. The models included terms for age, calendar year, a smooth function of the day of the year and an offset term for the population size to account for demographic changes, temporal trends in mortality and seasonality. The excess deaths were obtained by subtracting the number of observed deaths from the number of expected deaths.

Results:
As of March 2023, over 6.2 million COVID-19 deaths were registered globally (around 190,000 in Italy). In 2020, we estimated 99,341 excess deaths in Italy, 60,351 in 2021, and 66,303 in 2022. For the first 4 months of 2023, the number of observed deaths was slightly less than the number of expected deaths. The total excess from the beginning of the pandemic in Italy to the end of 2020 amount to approxi­mately 226,000 deaths, a figure that exceeded COVID-19 deaths by 36,000.

Conclusions:
Excess total mortality is a key metric to quantify the overall impact of the pandemic. However, the limited availability of data in some densely populated countries introduces significant uncertainty into any global estimates.