Following an abrupt end to the Chinese government’s strict lockdowns and “zero COVID” policy in December 2022, its citizens will be allowed to travel abroad for the first time since the pandemic began in 2020. In response, over a dozen countries have announced testing requirements and other restrictions on travelers from China.

The United States, Canada, Spain, France, Japan and the United Kingdom have cited concerns about a surge of COVID-19 infections in China, the potential risk of new variants emerging from its outbreak, in addition to a perceived reluctance by the Chinese government to share data with other countries among their reasons for implementing the testing policy.

[Related: What’s next for China’s zero COVID policy.]

Chinese government officials are pushing back against these restrictions. “Some countries have no scientific basis for restricting entries from China, and some excessive practices are even more unacceptable,” said Mao Ning, a foreign ministry spokeswoman, speaking at a news conference in Beijing on January 3. “We firmly oppose the practice of manipulating COVID prevention and control measures to achieve political goals, and will take corresponding measures in accordance with the principle of reciprocity according to different situations,” she added.

On December 28, the Centers for Disease Control and Prevention (CDC) announced that travelers from China, Hong Kong, and Macau will be required to present a negative COVID-19 test before entering the United States beginning on January 5, 2023. The CDC says the requirement for testing applies to air passengers regardless of their vaccination status and nationality, and will apply to travelers from China entering through a third country or those who connect through the US to other countries.

“Variants of the SARS-CoV-2 virus continue to emerge in countries around the world. However, reduced testing and case reporting in the PRC and minimal sharing of viral genomic sequence data could delay the identification of new variants of concern if they arise,” wrote the CDC in a statement. “Pre-departure testing and the requirement to show a negative test result has been shown to decrease the number of infected passengers boarding airplanes, and it will help to slow the spread of the virus as we work to identify and understand any potential new variants that may emerge.”

Similar restrictions have already been imposed in Italy and Japan, while India has mandated negative COVID-19 test reports and random screening for passengers arriving by air from China, Japan, South Korea, Hong Kong, and Thailand.

[Related: China approves world’s first nasal COVID-19 vaccine booster.]

The World Health Organization (WHO) has also urged Chinese officials to be more transparent on the country’s current surge of COVID-19 infections. The WHO requested more genetic sequencing data, data on hospitalizations, ICU admissions, and deaths, in addition to data on both the number of vaccinations delivered and vaccination status, especially in vulnerable people and those over 60 years old.

This lack of transparency surrounding COVID-19 data has health experts particularly concerned. “For the most part, we really don’t know what variants are circulating in China,” Andy Pekosz, a virologist at Johns Hopkins University in Baltimore, told CBS News. “That represents sort of a black box in terms of what we might be concerned about in terms of new variants in that country.”

However, Pekosz doesn’t believe that testing alone will be enough to stop a new variant from entering the US. “What you really need is a holistic approach. You need to know the sequences of the viruses that are there,” he said. “You need to know case numbers and hospitalization rates and how they are related to new variants. All of that information helps us to then prepare for a new variant if it were to arrive. Testing alone isn’t going to prevent a new variant from arriving here in the US.”

Parts of China have been fighting outbreaks of COVID-19 since the policy shift in December, but the severity of the outbreaks have been a guessing game.