A man wearing a face mask walks at a market amid the COVID-19 outbreak in Sanaa, Yemen, on May 31, 2020. (Photo by Mohammed Mohammed/Xinhua)

A vendor wearing a face mask waits for customers amid the COVID-19 outbreak in Sanaa, Yemen, on May 31, 2020. (Photo by Mohammed Mohammed/Xinhua)

Children wearing face masks ride a horse amid the COVID-19 outbreak in Sanaa, Yemen, on May 31, 2020. (Photo by Mohammed Mohammed/Xinhua)

A man wearing a face mask walks at a market amid the COVID-19 outbreak in Sanaa, Yemen, on May 31, 2020. (Photo by Mohammed Mohammed/Xinhua)