A woman takes the COVID-19 booster shot at the Tournament House in Pasadena, Los Angeles County, California, the United States, Aug. 19, 2021. (Xinhua)

A medical worker prepares the COVID-19 vaccines for local residents at the COVID-19 vaccination clinic in Pasadena, Los Angeles County, California, the United States, Aug. 19, 2021. (Xinhua)

A medical worker prepares the COVID-19 vaccines for local residents at the COVID-19 vaccination clinic in Pasadena, Los Angeles County, California, the United States, Aug. 19, 2021. (Xinhua)

Local residents come for the COVID-19 booster shots at the COVID-19 vaccination clinic in Los Angeles, the United States, Aug. 19, 2021. (Xinhua)