ISTANBUL ­— The Turkish government is expected to begin mass distribution of a COVID-19 vaccine produced by China’s Sinovac Biotech this week as questions remain over its efficacy rate.

The rollout is expected to begin Thursday or Friday if testing by the Turkish Medicines and Medical Devices Agency delivers positive results today. An interim analysis last month by Turkish researchers found the Sinovac vaccine to be 91.25% effective while preliminary tests in Indonesia showed a 65% efficacy rate, leading officials there to grant the vaccine emergency approval Monday.

Previously, final-stage trials in Brazil found the vaccine to be 50.38% effective, though Sinovac CEO Yin Weidong told reporters Wednesday the disparity was caused by the participation of high-risk medical workers in the Brazilian study.

The developments come as Turkey is expected to receive 10 million doses of the Sinovac vaccine in the next two weeks, adding to three million doses received late last month. Turkey has contracted to purchase a total of 50 million Sinovac doses. State officials have also agreed to procure 4.5 million doses of the Pfizer-BioNTech vaccine, which has been found to have a 95% efficacy rate.