A medical worker wearing protective gear waits for people to receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

Medical workers wearing protective gear walk at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

People walk after receiving a dose of a Covid-19 vaccine at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

People receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

A medical worker wearing protective gear waits for people to receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

A medical worker wearing protective gear waits for people to receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

Medical workers wearing protective gear walk at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

A man walks after receiving a dose of a Covid-19 vaccine at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

A medical worker wearing protective gear waits for people to receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)

People receive the COVID-19 vaccine, at Belgrade Fair makeshift vaccination center in Belgrade, Serbia, Tuesday, Feb. 9, 2021. China is ready to consider "vaccine cooperation" with Central and Eastern European countries, President Xi Jinping said Tuesday in a meeting held by video link with European leaders. Serbia has received 1 million doses of a Chinese-developed coronavirus vaccine and Hungarian and Chinese vaccine developers are cooperating. (AP Photo/Darko Vojinovic)