Women wearing face masks to help curb the spread of the coronavirus and a child walk by a billboard showing the words "All people participate in building a line of defense against the epidemic, please get the vaccine in time" on display outside a shopping mall in Beijing on May 24, 2021. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Andy Wong)

COVID-19 vaccine are produced at a factory of Chinese pharmaceutical company Sinovac in Beijing on Sept. 24, 2020. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)

A woman tends to a baby in a pram as a girl waits to cross a junction near a vaccination site in Beijing on May 11, 2021. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)

A child wearing a mask to protect from COVID-19 passes by a poster with the slogan "Receive COVID-19 vaccination, jointly built an Immunity Great Wall" in Beijing on Feb. 14, 2021. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)

Yin Weidong, CEO of the Chinese pharmaceutical company Sinovac, points to projection of COVID-19 infections and vaccinations at a briefing to journalists during a tour of a vaccine factory in Beijing on Sept. 24, 2020. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)

COVID-19 vaccine produced by Chinese pharmaceutical company Sinovac are displayed at the company's factory in Beijing on Sept. 24, 2020. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)

People carry their child wearing face masks to help curb the spread of the coronavirus head to a kindergarten in Beijing on June 9, 2021. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Andy Wong)

A woman and child wearing period costumes pass by a bus providing COVID-19 vaccination outside the Forbidden City in Beijing on April 14, 2021. If China is to meet its tentative goal of vaccinating 80% of its population against the coronavirus by the end of the year, tens of millions of children may have to start rolling up their sleeves. (AP Photo/Ng Han Guan)