City worker Carlos Ruiz delivers a tank of oxygen to a COVID-19 patient, in the Iztapalapa borough of Mexico City, Friday, Jan. 15, 2021. The city offers free oxygen refills for COVID-19 patients. (AP Photo/Marco Ugarte)

A person loads into the back seat of a car a tank filled with oxygen for a family member sick with COVID-19, in the Iztapalapa borough of Mexico City, Friday, Jan. 15, 2021. The city offers free oxygen refills for COVID-19 patients. (AP Photo/Marco Ugarte)

City worker Alexis Hernandez rides in the back of a cargo truck transporting tanks of oxygen for COVID-19 patients, in the Iztapalapa borough of Mexico City, Friday, Jan. 15, 2021. The city offers free oxygen refills for COVID-19 patients. (AP Photo/Marco Ugarte)

City worker Carlos Ruiz gives instruction to a COVID-19 patient after delivering a tank of oxygen to her home in the Iztapalapa borough of Mexico City, Friday, Jan. 15, 2021. The city offers free oxygen refills for COVID-19 patients. (AP Photo/Marco Ugarte)