SINGAPORE - The Sinovac vaccine carries some risk of a person being infected despite taking the jabs, based on evidence from other countries, Singapore's director of medical services Kenneth Mak said on Friday (June 18).

For instance, there has been a recent report of healthcare workers in Indonesia still being infected even after receiving the Sinovac vaccine, and in other countries, the authorities are starting to think about booster vaccinations just six months out from an original vaccination, Associate Professor Mak added.

"So it does give the impression that the efficacy of different vaccines will vary quite significantly," he said.

Prof Mak, speaking at a virtual Covid-19 multi-ministry task force press conference, noted that the Pfizer-BioNTech and Moderna vaccines Singapore is using are among those with the highest efficacy.

It was previously reported that the Pfizer-BioNTech and Moderna mRNA vaccines have consistently shown to be highly efficacious, with an efficacy rate of around 90 per cent.

The Sinovac vaccine has shown variable protection across multiple studies carried out internationally, with the most complete analysis showing a vaccine efficacy of 51 per cent.

Prof Mak said Singapore's Health Sciences Authority (HSA) has yet to approve Sinovac as there is still some critical data that the manufacturer has not provided to give the authorities the complete assurance about the quality and safety profile of the vaccine.

He added: "And because that data is still limited, HSA has not been able to make progress in converting Sinovac from simply a vaccine made available through the special access route into one that actually has that pandemic special access route (PSAR) approval."

Demand for the Pfizer and Moderna jabs - the two HSA-approved vaccines in Singapore - is also high, with many people waiting to book their appointments.

"But we are releasing the booking slots based on supplies," Health Minister Ong Ye Kung said, assuring that there will be sufficient supplies for the whole population to receive full protection.

"The question is really one of timing... whether we can work with the suppliers to see whether some of those (vaccines) can come earlier. And then we are in a better position to be able to open," he added.

Prof Mak said the two vaccines arrive in Singapore in batches on their own time, so supplies for each vaccine will vary at different times.

He added: "These vaccines are all HSA PSAR-approved. They're fine for our use, and it's okay to register for the Moderna vaccine... you don't have to wait for the Pfizer-BioNTech vaccine."