A resident receives a dose of COVID-19 vaccine in Pasadena, Los Angeles County, California, the United States, Jan. 15, 2021. (Xinhua)

A resident receives a dose of COVID-19 vaccine in Pasadena, Los Angeles County, California, the United States, Jan. 15, 2021. (Xinhua)

A nurse prepares to inject a dose of COVID-19 vaccine in Pasadena, Los Angeles County, California, the United States, Jan. 15, 2021. (Xinhua)

Residents receive COVID-19 vaccines in Pasadena, Los Angeles County, California, the United States, Jan. 15, 2021. (Xinhua)

A resident receives a dose of COVID-19 vaccine in Pasadena, Los Angeles County, California, the United States, Jan. 15, 2021. (Xinhua)