Epidemiological impact of revoking mask-wearing recommendation on COVID-19 transmission in Tokyo,Japan

Despite the global implementation of COVID-19 mitigation measures,the disease continues to maintain transmission.Although mask wearing became one of the key measures for preventing the transmission of COVID-19 early in the pandemic period,many countries have relaxed the mandatory or recommended wearing of masks.The objective of the present study was to estimate the epidemiological impact of removing the mask-wearing recommendation in Japan.We developed a model to assess the consequences of declining mask-wearing coverage after the government revoked its recommendation in February 2023.The declining mask-wearing coverage was estimated using serial cross-sectional data,and a mathematical model was devised to determine the age-specific incidence of COVID-19 using the observed case count in Tokyo from week of October 3,2022 to October 30,2023.We explored model-based counterfactual scenarios to measure hypothetical situations in which the mask-wearing coverage decreases or increases relative to the observed coverage.The results show that mask-wearing coverage declined from 97%to 69%by the week of October 30,2023,and that if the mask-wearing recommendation had continued,427 lives could have been saved in Tokyo.If the mask-wearing coverage had declined to 25%of the observed level,the model suggests there might have been 1587 additional deaths.Thus,revoking the mask-wearing recommendation had a substantial epidemiological impact.In future pandemics,our proposed approach could provide a realtime quantification of the effects of relaxing countermeasures.