Effectiveness of mask in COVID-19 pandemic in Japan

抄録

Background: The government of Japan had stopped to recommend to wear mask on March 13, 2023.

Object: The object of this study was to estimate effectiveness of mask to prevent for COVID-19 infection through comparison among before and after the stopping date.

Method: The effective reproduction number(R(t)) was regressed on dummy variable for after the stopped date as well as vaccine coverage, vaccine coverage with some delay, temperature, humidity, mobility, share of the mutated strains, counter measures including Go To Travel Campaign and an Olympic Games. The study period was February, 2020 through April 14, 2023, as of May 7, 2023.

Results: We selected the specification with 90 days lag of waning. In this specification, the second to the fourth vaccination coverage, the first to the third emergency of status, Goto Travel Campaign and Olympic games and the share of other minor mutated strains were significantly negative. Conversely, share of the alpha, delta, and BA2, BA5, and XBB.1.5 sublineage of omicron variant strain,

The estimated coefficient of after the stopped date for recommendation to wear mask was negative but insignificant.

Discussion: The obtained estimated results showed that mask may not have effectiveness to reduce infection of COVID-19. However, it might suggest that the most of Japanese have continued to wear mask without the government did not recommend after the stopped date.