Indonesian President Joko Widodo was shown receiving the country’s first CoronaVac, after the government authorized it for emergency use.

Mass public vaccination programs using a Chinese coronavirus vaccine are underway across Indonesia and Turkey, where tens of millions of people are expected to receive doses of the CoronaVac shot made by Beijing-based company Sinovac.

On Wednesday, Indonesian President Joko Widodo was shown receiving the country’s first CoronaVac shot, after the government authorized it for emergency use. While on Thursday, Turkish President Recep Tayyip Erdogan announced he had also received the vaccine.

But the rollouts come despite a growing number of questions over the effectiveness of the shot, which last week was revealed to have an efficacy rate of just 50.38% in late-stage trials in Brazil — significantly lower than earlier results showed. That rate only barely crosses the 50% efficacy threshold as set by the World Health Organization, and far lower than the 78% previously announced to much fanfare in China earlier this month.

The apparent discrepancy has led to concern among some scientists, and shaken international confidence in Chinese-made vaccines.

“Since many countries are planning to order, or have already ordered Sinovac’s vaccines, it might undermine people’s willingness to take them, because people may question the usefulness of the vaccines,” said Yanzhong Huang, a senior fellow for global health at the US based Council on Foreign Relations and expert on the Chinese health care system. “It could be a potential stumbling block.”

The Brazilian results suggest CoronaVac is far less effective than vaccines developed by Pfizer-BioNTech and Moderna, which have an efficacy rate of about 95%. Russia says its Sputnik V vaccine has an efficacy of 91%, while the UK’s vaccine, developed by Oxford University and AstraZeneca, has an average efficacy of 70%. The Sinovac vaccine has a lower efficacy rate than its domestic Chinese competitor, developed by the state-owned Sinopharm, which it says has a 79.34% efficacy.

Under review

The Sinovac and Sinopharm vaccines have been regarded as potentially affordable and easily distributed vaccine candidates. Unlike the Pfizer-BioNTech and Moderna vaccines, the Chinese shots do not require expensive cold storage.

Sinovac has agreements in place with at least six governments, with plans in place to provide 46 million doses of its CoronaVac vaccine to Brazil, 50 million doses to Turkey and 7.5 million doses to Hong Kong. It will also supply 40 million doses of vaccine bulk — the vaccine concentrate before it is divided into vials — to Indonesia for local production.

Thailand has ordered 2 million doses of CoronaVac and expects to receive the first 200,000 doses in February, while the Philippines has ordered 25 million doses, of which the first batch is also expected to arrive next month, according to Reuters.

However, following the release of the Brazilian trial data, other countries are now reexamining potential plans.

Singapore’s Health Minister said officials would review Sinovac’s vaccine before any rollout to its citizens. Singapore has not approved the vaccine but does have a purchase agreement with the company. Health Minister Gan Kim Yong said the vaccine would need to go through a regulatory process and authorization by Singapore’s Health Sciences Authority, according to the Straits Times.

Malaysia also said it would seek more data from Sinovac before it approved and purchased supplies, Reuters reported — while in Hong Kong, which has signed a deal with Sinovac, a senior medical adviser said an expert panel would review every vaccine based on clinical trial data.

Even though Brazil’s health agency regulator, Anvisa, voted to approve emergency use authorization of Sinovac’s CoronaVac vaccine on Sunday, it said it did not have access to important data about the vaccine on the Phase 3 study, such as the duration of protection provided by the vaccine and its effect on the elderly and other specific groups, such as people with comorbidities.

Brazil’s national vaccination program is set to begin on January 20, according to the health ministry.

And while governments in Thailand and the Philippines have so far publicly backed the Sinovac shot, politicians in both countries have questioned their rollout plans. In response to the concerns, Thai regulators have asked Sinovac to provide more detailed information on the clinical trials.

On Wednesday, Sinovac defended the safety and efficacy of its vaccine. “These Phase III clinical trial results are sufficient to prove that CoronaVac vaccine’s safety and effectiveness are good around the world,” company chairperson, Yin Weidong, said in a news conference, according to Reuters.

Originally published at CNN