Fragmental releases of efficacy data for the Covid-19 vaccine developed by China’s Sinovac could undermine confidence in the shot, experts warned, as several countries prepare for mass inoculations with the vaccine, Reuters reports.

Turkish researchers said on Thursday Sinovac’s CoronaVac was 91.25 per cent effective based on an interim analysis only to see a confusing readout the same day from Brazil which said the vaccine’s efficacy was between 50pc and 90pc. Brazil has also delayed release of its efficacy data on the vaccine three times, as Sinovac seeks to consolidate data from global trials that include Indonesia, Turkey and Chile.

The efficacy data is being closely watched as many developing countries have signed deals to use the Sinovac vaccine which is easier to store and transport than rival shots developed by Pfizer and its partner BioNTech and Moderna.

“You really want the data to be compelling at first presentation; this is what Pfizer and Moderna achieved, AstraZeneca less so,” said Jerome Kim, head of the International Vaccine Institute, a Seoul-based non-profit agency devoted to research in vaccine. “With multiple ‘leaks’ of data and suggestions of this or that you don’t see the same effect with Sinovac; perhaps the final presentation in January will be more compelling.”

Sinovac had no immediate comment.