Scientists are urging China to look for alternatives to its two homegrown Covid-19 vaccines to tackle its Omicron outbreak, amid mounting concerns about the jabs’ efficacy against the variant.

The country is struggling with two problems as it faces its worst Covid-19 surge since the start of the pandemic: the sluggish take-up of booster doses — authorities said this week that only 57 per cent of people over 60 have been fully vaccinated with three jabs — and homegrown vaccines that are much less effective than foreign-produced jabs.

Studies have recommended that China’s Sinovac jab be boosted with a more effective shot, such as one of the mRNA vaccines produced by Germany’s BioNTech and Moderna of the US. With little data on China’s Sinopharm jab, many researchers believe it will also struggle against Omicron.

Eric Topol, director of the Scripps Research Translational Institute, said the data was “limited” but the inactivated vaccines, which are made using a dead part of the virus, were less effective than their rivals and declined further with time.

“The vaccines were at 60 per cent efficacy, it was never rosy, but Omicron really exposed the problem,” he said.

China may have to overcome its reluctance to approve a foreign-made vaccine to tackle the latest outbreak, as well as rapidly rolling out boosters of its domestic shots. Otherwise, it will probably have to impose stricter — and costly — lockdowns to prevent a potentially huge death toll.

A study from the University of Hong Kong published last month found that people over 60 who had received two doses of Sinovac’s vaccine CoronaVac were three times more likely to die from Covid compared with people who received two doses of the BioNTech/Pfizer vaccine.

The paper, which has yet to be peer-reviewed, concluded a third dose of either vaccine provided high levels of protection against severe disease.

Sinovac did not respond to a request for comment.

Ben Cowling, an epidemiologist at HKU, said the third shots for Chinese vaccines should be seen as simply completing a minimum course rather than a “booster”.

“It’s important to know that the World Health Organization recommends three doses of inactivated vaccine for the elderly. They said two is not enough,” he said.

Crucially, the HKU paper said it was too early to tell how long the protection from three doses lasted. Jin Dong-yan, a virologist at the university, said many of the third shots considered in the paper were given just before this year’s Covid wave in Hong Kong, so it did not demonstrate how CoronaVac held up against Omicron over time.

Concerns that any benefits would wane rapidly have prompted many scientists to suggest that countries dependent on the inactivated shots — which China sent to low and middle-income nations as part of its vaccine diplomacy strategy — should consider boosting with jabs made on other platforms.

In Brazil, a study that collected evidence from September to March found a CoronaVac booster provided limited additional protection but a Pfizer booster offered protection against severe disease for at least three months.

A Yale University study went further, suggesting that people who received two inactivated doses may need two mRNA boosters.

Akiko Iwasaki, a professor of immunobiology at Yale and an author of the paper, said the inactivated vaccines tended not to elicit much response from one of the immune system’s T-cells, known as CD8, meaning long-term protection might not be reliable.

“So people who have had two Sinovac vaccines would need two booster doses of mRNA just to bring the neutralising titres [numbers of antibodies] to a similar level of three mRNA vaccines,” she said.

Many countries are boosting with alternative jabs. Indonesia, Pakistan and Brazil were among the largest recipients of Chinese vaccines, but all have used far fewer as boosters, according to health data analytics firm Airfinity.

Julio Croda, an infectious disease specialist at Brazil’s Fiocruz, a biosciences research institute, said most Latin American countries recommended other vaccine platforms, especially for older people.

But Croda added that some countries suffered from a lack of access to alternatives to inactivated vaccines, as well as having a smaller share of the global vaccine supply overall.

Even before BioNTech announced its partnership with Pfizer, the company signed an alliance with China’s Fosun Pharma in March 2020 to provide any successful Covid mRNA shot to the country. But more than two years later, China has not approved the BioNTech vaccine for use on the mainland.

Jin said Chinese authorities should approve it “without delay”. 

Chinese companies have been working on their own mRNA Covid vaccines. CanSino Biologics recently received permission to start trials of its mRNA shot in the country. Sinopharm is also developing an mRNA candidate.

But Jin said no one knew if they would work as well. The mRNA vaccines appear to be simple, using genetic code to teach the immune system to recognise the virus’s spike protein, but there are many patent-protected innovations behind the successful jabs. CureVac, a German vaccine maker, abandoned its first-generation mRNA jab last year because of a lower efficacy rate than the market leaders.

The Chinese efforts suffered a setback when an early study showed one potential mRNA jab, developed by Suzhou Abogen Biosciences, appeared not to elicit many antibodies to tackle Omicron.

Brian Yang, a health expert at research group Informa, said the Chinese authorities were pushing hard for a domestic vaccine but that investing in mRNA would not necessarily translate into success.

“China always believes that if you put in enough money and the right expertise you can make it work, but mRNA takes a lot of accumulated knowledge,” Yang said.