A Cambodian woman receives her first dose of Sinovac COVID-19 vaccine at an inoculation site in Phnom Penh, Cambodia on April 1, 2021. Cambodia on Thursday started to inoculate its citizens with the Sinovac COVID-19 vaccine developed by the Chinese biopharmaceutical company Sinovac Biotech. (Photo by Sovannara/Xinhua)

A Cambodian nurse pumps the Sinovac COVID-19 vaccine with a syringe at an inoculation site in Phnom Penh, Cambodia on April 1, 2021. Cambodia on Thursday started to inoculate its citizens with the Sinovac COVID-19 vaccine developed by the Chinese biopharmaceutical company Sinovac Biotech. (Photo by Sovannara/Xinhua)

A Cambodian woman receives her first dose of Sinovac COVID-19 vaccine at an inoculation site in Phnom Penh, Cambodia on April 1, 2021. Cambodia on Thursday started to inoculate its citizens with the Sinovac COVID-19 vaccine developed by the Chinese biopharmaceutical company Sinovac Biotech. (Photo by Phearum/Xinhua)

A Cambodian nurse pumps the Sinovac COVID-19 vaccine with a syringe at an inoculation site in Phnom Penh, Cambodia on April 1, 2021. Cambodia on Thursday started to inoculate its citizens with the Sinovac COVID-19 vaccine developed by the Chinese biopharmaceutical company Sinovac Biotech. (Photo by Sovannara/Xinhua)