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This photo taken on December 20, 2021 shows a medical worker taking a sample from a resident, to be tested for the Covid-19 coronavirus at a residential community in Xi'an, in China's northern Shaanxi province, after the detection of more than 40 new cases raised concerns of wider transmission ahead of a busy travel season. - China OUT (Photo by AFP) / China OUT (Photo by STR/AFP via Getty Images)

This photo taken on December 20, 2021 shows a medical worker taking a sample from a resident, to be tested for the Covid-19 coronavirus at a residential community in Xi'an, in China's northern Shaanxi province, after the detection of more than 40 new cases raised concerns of wider transmission ahead of a busy travel season. - China OUT (Photo by AFP) / China OUT (Photo by STR/AFP via Getty Images)