BackgroundPrioritization for COVID-19-related health policies usually considers age and certain other characteristics, but sex is rarely included despite the higher risk of severe disease in men. The aim of this study was to compare the impact of sex and age on the severity of COVID-19 by estimating the age difference in years for which the risk for men vs. women is the same.MethodsWe analyzed 23,414 Japanese COVID-19 in-patients aged 20-89 years (13,360 men and 10,054 women). We graded the severity of COVID-19 (0 to 5) according to the most intensive treatment required during hospitalization. The risk of grade 2/3/4/5 (non-invasive positive pressure ventilation / invasive mechanical ventilation / extracorporeal membrane oxygenation / death), grade 3/4/5, and separately grade 5 was analyzed using a multiple logistic regression model.ResultsThe risk of grades 2/3/4/5, 3/4/5 (primary outcome), and 5 for men relative to women was 2.76 [2.44-3.12], 2.78 [2.42-3.19], and 2.60 [2.23-3.03] (odds ratio [95% confidence interval] adjusted for age and date of admission), respectively. These risks for men were equivalent to those for women 14.1 [12.3-15.8], 11.2 [9.7-12.8], and 7.5 [6.3-8.7] years older, respectively.ConclusionsThe risks of worse COVID-19 prognosis (grades 3/4/5) in men were equivalent to those of women 11.2 years older. Reanalyzing data extracted from four previous studies also revealed a large impact of sex difference on the severity of COVID-19. We should pay more attention to sex differences to predict the risk of COVID-19 severity and to formulate public health policy accordingly.