The calculation of disease burden, based on the DALY index (YLL, YLD) since its development in the 1990s, has been widely used to estimate the impact of lower respiratory system infections (14, 15). In this study, the years of life lost based on COVID-19 were investigated.
The results of our study showed that the mean age of men at the time of death due to COVID-19 was 66 years and in women was 67 years and the sex ratio was 1.5 (men/women). The mean age at death for men and women in Italy was 79.5 and 106 years, respectively(16). Another study conducted in Italy(17) showed that the mortality rate was higher in men than women, which is consistent with our study. This difference may be due to reasons such as immunological differences between men and women, differences in lifestyle (e.g. more smoking in men) and more presence of men in society.
Mortality rate
The results of our study showed that the mortality rate due to COVID-19 was 63.98 per 100,000 people, which has been steadily increasing with age. The mortality rate varies from region to region. Estimates show that worldwide mortality rate due to COVID-19 is about 3% (18). Studies shown that mortality rate in China is 7.3, in uk 8.8, Japan 10.7 and India 7.3 per 1000 (19). Based on other study in china, mortality rate is 3.6%(20). In Italy, the rate varied from 3–24% (in the elderly) (21). Generally mortality rate due to covid 19 is very different in different countries and the lowest and highest mortality rates of 1.2% and 12% are in Qatar and Nigeria, and on average in world 8% respectively (19).
The mortality rate in Iran is consistent with other countries and is almost in the middle of estimates reported in other countries. The reasons for these differences may be due to several factors, such as differences in data quality, differences in data recording, differences in age groups, and so on.
YLL by age and gender groups
The results of our study showed that the highest YLL due to COVID-19 in men and women was in the age group of 70–79 years. In both genders, the lowest YLL was in the age group of 10–19 years (Fig. 2).
In a study conducted to determine Years of Life Lost Attributable to COVID-19 in High-incidence Countries showed that YLLs due to COVID-19 were higher among males than among females and higher in those aged ≥ 60 years than in younger individuals (22).
In Korea, the highest YLL for men and for women occurred in the age group of 70–79 and over 80 years, respectively (9). In Italy, the highest and lowest YLL was in the age group of 70–79 and 10–19 years for both genders (17).
According to a meta-analysis study, in most countries the death rate is higher for men than for women. In some countries, the death rate from men to women is six times higher. But in some countries, such as Ethiopia, the death rate is higher for women than for men. Overall, the overall mortality rate from COVID-19 is 1.4 in men compared to women (23).
The results of the mentioned studies are consistent with the lowest age group that had the lowest YLL, but in terms of age group with the highest YLL. This means that the Iranian population (Fars province as a representative of the Iranian population) had the highest morbidity and mortality at younger ages (60–69 years). The reasons for this may be due to the greater presence of men in society and the economic activity of men at this age. The results of the mentioned studies are in line with our study in terms of age group with the lowest YLL, but not in terms of age group with the highest YLL. This means that the Iranian population at the younger age (69 − 60 years) had the highest morbidity and mortality.
The strengths of the study are discussed as follows. First, in this study, we used two methods to calculate the years of life lost to COVID-19. Second, we calculated age standardized rates. Third, there were no missing cases in this study.