Countries around the world soon implemented increased testing requirements for arrivals from China, which have gone into effect during the run-up to heightened travel during the Lunar New Year holiday in late January. The new rules come into effect amid reports of overflowing hospitals and medicine shortages in China after it reversed its “zero covid” policy.

Among the strictest are policies in Italy, South Korea, Japan and Taiwan, which require on-arrival testing for passengers from China. The United States requires proof of a negative test before departure, while other countries are testing wastewater from aircraft on flights originating in China.

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Official data showed infection rates of more than 20 percent among travelers from China to neighboring South Korea and Taiwan in the first week of January.

Data from the Korea Disease Control and Prevention Agency obtained by The Washington Post showed a 23.2% infection rate for short-term visitors from China to Korea (or 314 out of 1,352 tested at the airport) from Jan. 2 to Jan. 6. The KDCA expects to publish data on all travelers from China next week, an official told The Post.

According to the Taiwan Centers for Disease Control, from Jan. 1 to Jan. 5 about one in five travelers (21%) from mainland China tested positive for covid, or 1,111 out of 5,283 arrivals.

On Friday, Japan’s Ministry of Health, Labor and Welfare reported that about 8 percent of visitors from China from Dec. 30 to Jan. 6 had tested positive for covid, or 408 out of 4,895 arrivals. Data from Italy was not immediately available.

“These numbers are certainly [the] tip of the iceberg, highlighting the immense size of infections in China,” Yanzhong Huang, Senior Fellow for Global Health at the Council on Foreign Relations, wrote in an email, responding to early reports suggesting an infection rate of 20 to 50 percent among Chinese travelers.

The numbers are particularly high, “if we consider that people typically would not travel overseas unless they feel well and healthy, or do not show symptoms,” he said.

However, given the high levels of exposure to covid in many countries, “it is not reasonable to view [visitors from China] as diseased or dangerous,” he said.

Benjamin Cowling, an epidemiologist at the University of Hong Kong, called the high early infection rates “completely consistent with forecasts that the majority of the population of major cities have already been infected.” He said in an email that people can remain positive on PCR tests for weeks.

“Since most infections have occurred in late December and early January, and more than half of the population in major cities have already been infected, it is quite plausible that high percentages of travelers have been testing positive,” he wrote. “Those testing positive will mostly have recently recovered from infection rather than still being sick and/or contagious.”

Last month, China partly lifted domestic restrictions in a move seen as a response to a rare public backlash directed at the country’s notoriously stringent zero-covid policy.

On Sunday, China will end extensive quarantine requirements for inbound passengers, a decision that will mostly benefit Chinese who want to leave or Chinese nationals abroad who want to return. Mainland China is still closed to foreign tourists.

The move comes just weeks before the Lunar New Year, which begins on Jan. 22. Before the pandemic, travel during China’s “Golden Week” national holiday was believed to be the world’s largest annual human migration.

The Chinese holiday “will ensure that the virus reaches every last corner of the country by the end of January,” Cowling said.

Huang said the holiday season will encourage “retaliation tourism” — travel making up for time lost during the pandemic — and is likely to cause a peak in outbound infections. But he also said it is unlikely that travelers leaving China will make the virus worse elsewhere.

“So far, there is no evidence of emerging new subvariants from China,” he said. “Given that most of these countries have learned to coexist with covid-19, the influx of Chinese visitors are not going to lead to spike of cases in these countries.”

The changes also come amid wider scrutiny of Beijing, which has stopped counting asymptomatic covid cases. The World Health Organization has questioned China’s data and requested more information from Beijing.

The testing requirements targeting arrivals from China has drawn ire from Chinese authorities. “Some of these measures are disproportionate and simply unacceptable,” a Chinese Foreign Ministry spokesperson said at a Jan. 3 news conference. “We firmly reject using COVID measures for political purposes and will take corresponding measures in response to varying situations based on the principle of reciprocity.”

Julia Mio Inuma in Tokyo and Lily Kuo in Taipei, Taiwan, contributed to this report.