What's behind Sinovac's vaccine varying efficacy rates?

Sinovac Biotech Ltd is a Beijing-based biopharmaceutical company responsible for CoronaVac, an inactivated vaccine.

An inactivated vaccine contains the virus that has been killed, exposing it to the body’s immune system. This vaccine may not provide immunity or protection as compared to live vaccines, hence several doses over time are needed to achieve immunity against diseases.

Inactivated vaccines have been used in the past to protect against diseases such as Hepatitis A and rabies.

Several countries have already ordered and even administered the Sinovac’s vaccine including Malaysia, Indonesia, Turkey, Singapore, and the Philippines.

A recent finding by researchers from Butantan Institute in Brazil found that the Sinovac’s vaccine only to be 50.4 per cent effective in protecting against the virus.

The number is significantly lower than the efficacy levels previously reported last week by the institute at 78 per cent.

Researchers in Turkey and Indonesia had also announced higher effectiveness rates but those studies were far too small to be conclusive.

Researchers in Turkey said it is 91.25 per cent effective based on data from 1,322 people (of 7,000 volunteers), whereas researchers from Indonesia said the vaccine is 65 per cent effective based on trials involving some 1,600 people.

While the rate of efficacy may typically not be ideal, global health authorities have said any vaccine that is at least 50 per cent effective would still be useful in fighting the virus.

To compare, seasonal flu vaccines typically have around 40 to 60 per cent effectiveness and are still widely administered around the world, despite the scepticism of them actually working.

Sinovac, responding to the results announced, has labelled them as misleading.

“These Phase III clinical trial results are sufficient to prove that CoronaVac vaccine’s safety and effectiveness are good around the world,” Sinovac Biotech Chairman Yin Weidong told a news conference.

“We have accelerated the ramping up of production capacity.”

Meanwhile, World Health Organisation (WHO) Director-General Tedros Adhanom Gebreyesus announced on Monday that the organisation is currently working with Sinovac and Sinopharm to assess compliance of the vaccines with international quality manufacturing practices ahead of potential emergency use listing by WHO.

Indonesia has already received the third batch of Sinovac vaccines, an additional 15 million doses on top of the 3 million it already received, as the country kickstarted its mass vaccination program with the vaccine.

The Thailand Ministry of Public Health on the one hand has decided that it will inquire about the effectiveness of the vaccine from Sinovac itself to seek detailed information on the issue.

Thailand is expecting to receive 2 million doses of the vaccine late next month.

Turkey which received its first shipment of the Sinovac vaccine, consisting of 3 million doses, last month has started its nationwide inoculation program after Turkish authorities gave the go-ahead for the emergency use of the vaccine.

The country is scheduled to get a total of 50 million doses of the vaccine.

Singapore’s Health Minister Gan Kim Yong said on Wednesday (13 Jan) that the vaccine will have to go through regulatory scrutiny and authorisation by Singapore's Health Sciences Authority (HSA) before it can be rolled out to the public.

Singapore has so far only authorised the Pfizer-BioNTech vaccine.

Science, Technology and Innovation Minister Khairy Jamaluddin has said that Malaysia will first review the clinical data and that it will only go ahead with procurement if it satisfies the safety and efficacy standards of local regulators. On Tuesday, Malaysia's pharmaceutical group Pharmaniaga Bhd announced that it had signed a deal with Sinovac to purchase 14 million doses of COVID-19 vaccines and will manufacture it domestically.

The company has the capacity to manufacture two million doses of vaccine a month beginning in March. The vaccine is expected to be ready for distribution by the end of March.