Home / Science / Health /  As delta variant spreads, China lacks data on its Covid-19 vaccines

The spread of the Delta variant is raising fresh concerns about the efficacy of Chinese vaccines, which have been central to inoculation efforts in the developing world, as recent data shows the protection provided by Western vaccines waning against the highly contagious variant.

Chinese officials have been analyzing data from an outbreak of the Delta variant in southern China last month, while Sinopharm and Sinovac Biotech Ltd., the country’s leading Covid-19 vaccine developers, have said they are studying Covid-19 variants, including via lab experiments. Both companies have suggested that a third booster shot may be needed to boost protection after their current two-dose regimens.

A sales executive at Sinovac, who declined to be named, says trying to figure out how much protection its vaccine, CoronaVac, offers against Delta has become a top priority for the company, although setting up new studies abroad could take months.

The efficacy of the Chinese vaccines against the Delta variant, which has now spread to at least 98 countries, will affect how soon China can open its borders and impact the course of the pandemic throughout much of the developing world, where many countries are reliant on Chinese shots.

In China, which has yet to approve any foreign vaccine against Covid-19, more than 40% of its 1.4 billion people had been fully vaccinated as of June 24. The country is still relying on some of the strictest pandemic control measures in the world to control outbreaks.

The southern Chinese city of Guangzhou is constructing a quarantine facility for international travelers that will be able to isolate 5,000 people. Authorities this week imposed a lockdown on the southwestern city of Ruili, where officials suspect the Delta variant may be present in a new outbreak.

Indonesia, one of the world’s most populous countries, is largely relying on Sinovac. The country, with around 5% of its population fully vaccinated, is now facing a surge driven by the Delta variant that is overwhelming its healthcare system. The Indonesian Medical Association’s Covid-19 mitigation group said in June that at least 10 of 26 doctors who had died so far that month had received two doses of Sinovac.

Data has already shown that Western vaccines are less effective at protecting against infections caused by Delta. Israel said that data there showed a vaccine developed by Pfizer Inc. and BioNTech SE protected 64% of fully vaccinated people during an outbreak of the Delta variant, down from 94% in earlier outbreaks.

The initial clinical trials for the Chinese vaccines—before the Delta variant started spreading—produced a range of results, but the efficacy levels for both Sinovac and Sinopharm were lower than the mRNA vaccines by Pfizer and Moderna Inc. A Brazil study found Sinovac to be only 51% effective against symptomatic infections.

Both Chinese vaccines have been found to be highly effective at preventing the severe cases of Covid-19 or hospitalization. The World Health Organization has approved both vaccines for emergency use, but its threshold to qualify vaccines for widespread use is 50% efficacy.

“If there’s a drop, that’s got to be below 50%," said Yanzhong Huang, a senior health fellow at the Council on Foreign Relations based in Washington. “I think that’s the reason they don’t want to reveal that true protective rate against the variant."

Sinovac and Sinopharm didn’t respond to requests for comment.

Chinese health experts have so far said little about how well China’s vaccines work against the Delta variant. Feng Zijian, a senior official at the Chinese Center for Disease Control and Prevention, is the only high-level Chinese health official who has said publicly that the Delta variant has reduced the efficacy of Chinese vaccines, although he maintains the vaccines still work. The National Health Commission referred to Mr. Feng’s comments and declined to comment further.

One of China’s leading epidemiologists, Zhong Nanshan, has projected confidence in Chinese vaccines’ ability to prevent the spread of the Delta strain, but he has given differing preliminary estimates on efficacy levels. He told state-owned Xinhua News Agency last month that based on more than 100 patients with the Delta strain in Guangzhou, Chinese vaccines—including shots by Sinovac and Sinopharm—are 69% effective against preventing infection among close contacts, 73% effective against pneumonia caused by the coronavirus and 95% effective against serious illness.

On the same day, he told state broadcaster China Central Television that, based on more than 160 Delta cases in Guangzhou, Chinese vaccines were more than 60% effective against infection by the Delta strain and close to 80% effective for severe illness associated with the strain.

He didn’t specify which vaccine he was referring to or say what kind of study the figures were based on. In an email to The Wall Street Journal, he said the figures were calculated based on “different baseline figures," without elaborating.

The efficacy of the Chinese vaccines is a sensitive topic in China. Their development and distribution globally has been a source of national pride, and they have already faced criticism and questions internationally over their initial clinical trial data.

One problem for Chinese health officials is that the Delta strain isn’t circulating widely enough in the country for vaccine makers to conduct a domestic study, meaning that Chinese researchers would need to seek data from countries like the United Arab Emirates and Indonesia, which have used Chinese shots widely and now are dealing with the Delta strain.

The sales executive at Sinovac said the company’s vaccine could face stiff competition in the coming months from shots that have demonstrated effectiveness against the Delta variant. In addition to the recent data from Israel, England’s public-health agency had earlier estimated that full vaccination using shots by Pfizer or AstraZeneca PLC reduced the risk of symptomatic Covid-19 with Delta by 79%.

Pfizer said Thursday that it would seek permission from U.S. regulators to distribute a booster shot to protect against new strains of the coronavirus. The company said it planned to begin clinical trials in August for a new version of its vaccine to protect against the Delta variant.

Chinese health officials have said they can cope with mutations by using new strains to make their vaccines, which are based on inactivated viruses. Protection by shots currently in use lasts for at least six months, according to pamphlets distributed by Sinovac and Sinopharm for their vaccines. The Chinese government hasn’t given guidance on how long protection lasts.

CanSino Biologics Inc., a Chinese vaccine maker that has distributed its one-shot regimen to developing countries, is also studying the Delta variant and a second booster shot, according to people familiar with the matter.

Shenzhen Kangtai Biological Products Co., whose Covid-19 vaccine was the sixth shot to be approved for emergency use by Chinese regulators in May, said last month that it is collaborating with a hospital in Shenzhen to develop a vaccine aimed at variants including the Delta strain. It will take at least three months before the first phase of clinical trials can start. The drugmaker’s first approved Covid-19 shot was an inactivated-virus vaccine and put into use before conclusive evidence on its efficacy was published.

—Raffaele Huang contributed to this article.

Write to Chao Deng at

Corrections & Amplifications

Chinese authorities this week imposed a lockdown on the southwestern city of Ruili. An earlier version of this article incorrectly spelled the city Ruli. (Corrected on July 9)

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