Costa Rica said Wednesday that will not purchase the Sinovac vaccine from China.
Officials said that data showed that it was not effective enough against the coronavirus.
Some places using China's other vaccine - Sinopharm - have had unexpected surges in virus cases.
Costa Rica's vaccination advisory board turned down China's Sinovac vaccine, describing the shot's efficacy as too low.
The National Commission on Vaccination and Epidemiology (NCVE) of Costa Rica said on Wednesday that negotiations with Sinovac, the vaccine's manufacturer, should be stopped.
It is the latest step in a wider wave of scrutiny for Chinese-made vaccines, which also include the Sinopharm shot.
According to the World Health Organization (WHO), the Sinovac's efficacy is 50.7%, when it comes to preventing symptomatic disease - significantly lower than Western-made shots.
Costa Rica can only approve vaccines with an efficacy above 60% following a resolution passed in April, prompting the country to reject Sinovac.
Another factor that played in Costa Rica's decision was that no data about the vaccine's efficacy has been published or submitted to the scrutiny of peers, according to Costa Rican vaccine official Roberto Arroba Tijerino.
The news came after the WHO vetted the Sinovac shot by giving it its Emergency Use Listing on June 1 based on results from a Brazilian trial, run on 12,000 health workers.
In that trial, the vaccine's efficacy was 50.7% against symptomatic disease, and 100% protective against hospitalization.
Broader questions about China's vaccine efficacy are circulating, as countries using the shot are seeing different results.
Another trial, run in Turkey, found the vaccine to be 83.5% effective at preventing symptomatic COVID-19. But that data has not been seen by the WHO.
Real-world data coming out of Indonesia, based on 128,000 health workers who received the shot in Jakarta, the capital of Indonesia, found the vaccine to be 94% effective. But this was found at a time when cases in the country were low, and on a relatively young population, with an average age of 31.
Country-wide data coming out of Chile indicates the shot might not be so protective. Even though the country had vaccinated 60% of its population, more than 93% of which were Sinovac's shots, Chile saw a sharp surge in cases in April.
The NCVE has said that if new data is presented to the WHO, it might change its mind.
As Insider reported this week, scrutiny of Chinese-made vaccines stepped up after three nations extensively using the Sinopharm shot - Bahrain, the Seychelles, and Mongolia - started noticing new spikes in cases even among some people who had taken the vaccines.
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