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The main Chinese vaccines appear to be working well against the Delta variant—but not as well as some of their foreign counterparts.

Recent studies suggest that China’s main vaccines from private maker Sinovac and state-owned firm Sinopharm are highly effective in preventing severe illness and death among those fully vaccinated. The studies provide backing for the World Health Organization’s May and June approvals of the jabs from the two Chinese vaccine producers.

Still, new studies have questioned the efficacy of the Chinese vaccines in comparison with other vaccines from makers like Germany’s BioNTech, the U.S.’s Moderna, and the U.K.’s AstraZeneca.

The evidence has come out as more countries have begun to lessen their reliance on imports of Chinese vaccines.

This week, Abu Dhabi, the capital of the United Arab Emirates, announced that it would require citizens fully vaccinated with Sinopharm jabs to get a third booster dose of Sinopharm or another vaccine. Brazil and Turkey have similarly opted for booster shots. Thailand is employing mix-and-match strategies with Western jabs to bolster the efficacy of Chinese vaccines. Malaysia has begun to phase out the use of Sinovac’s vaccine owing to questions about its efficacy.

But based on recent studies, experts say that China’s main vaccines are still providing people with a level of protection against the Delta variant. The scientific consensus remains that getting a Sinopharm or Sinovac jab is far better than getting no vaccine at all.

The studies

In China, researchers recently found that the Sinovac and Sinopharm vaccines had a combined efficacy of 70% in preventing COVID-19 infections during a Delta-driven outbreak in the southern city of Guangzhou.

The study, which has not yet been peer-reviewed, tracked over 10,000 people infected and their close contacts in an outbreak that infected 167 people with the virus. The study also showed that the vaccines were 100% effective in preventing severe cases and deaths.

“You have to take the results with a grain of salt because it is based on a very small sample size,” says Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations. “They might have overestimated the efficacy rate of the Chinese vaccines.”

In another recent preprint study from Bahrain, government researchers in partnership with Columbia University recently examined how China’s Sinopharm COVID-19 vaccine performed in comparison with Russia’s Sputnik V, Germany’s BioNTech, and the U.K.’s AstraZeneca. The study was conducted from May until August, tracking national data related to vaccine uptake, cases, hospitalizations, and deaths related to COVID-19, and coincided with the emergence of the Delta variant in Bahrain.

The results showed that recipients of the Sinopharm vaccine, and especially older populations, faced a higher risk of breakthrough infections, hospitalizations, and deaths, compared with people vaccinated with one of the other vaccines.

But even as Sinopharm’s vaccine may not be performing as strongly as its counterparts, the data revealed it to be effective in stopping some infections and deaths among those vaccinated.

“The hospitalized cases are mostly the unvaccinated” in the Bahrain study and worldwide, says Ashley St. John, an associate professor of immunology at Duke-NUS Medical School in Singapore. “While the various vaccines have differing efficacy, all of the WHO-approved vaccines provide some degree of protection from severe disease.”

Another recent study has suggested that China’s Sinovac vaccine may similarly provide less protection to elderly populations. Now, governments may consider changing their strategies of how to deploy the jabs.

A Brazilian preprint study published last week tracked 61 million people in Brazil from January to June, comparing infection, hospitalization, and death rates between unvaccinated individuals and those who received Sinovac or AstraZeneca jabs.

The study found that people fully inoculated with Sinovac reduced their risk of infection by 54% and risk of death by 74% compared with unvaccinated populations. Still, the AstraZeneca vaccine appeared to offer more protection, reducing the risk of infection by 70% and the risk of death by 90%. Sinovac’s efficacy also waned in older populations, reducing the risk of death by only 35% in populations over 80.

St. John says the study indicates that Sinovac’s vaccine is effective, but should perhaps be concentrated among younger populations.

“Where available, the elderly should be prioritized for vaccines that protect better in this demographic group,” says St. John. “Boosting the vaccine, potentially with another type of vaccine, could help.”

Global reach

But even as real-world studies indicate that China’s vaccines are not as effective as ones deployed from foreign counterparts, China’s vaccines are playing a critical role in getting the world vaccinated.

As of July, Sinovac and Sinopharm were the No. 1 and No. 3, respectively, most used vaccines in the world, according to Airfinity. The two manufacturers have also delivered 693 million shots to foreign countries while supplying the bulk of the 2 billion doses China has delivered domestically.

And the shots are providing some level of protection to billions worldwide in places that might not otherwise have access to vaccines.

The inequality in vaccine access is stark, as less than 2% of adults in low-income countries have been fully vaccinated, according to the WHO. Meanwhile, wealthy places like Israel, the U.S., and the European Union are rolling out, or preparing to roll out, booster doses in coming months.

“Vaccinating the unvaccinated in the U.S. and worldwide would likely have a greater benefit [than using booster shots in wealthy countries] on reducing transmission, reducing the emergence of new variants, and alleviating the burden on health care systems,” says St. John.

If wealthy nations continue to hoard doses, China, with the capacity to produce 5 billion vaccines per year, has enough supply to close the gap. Both Sinovac and Sinopharm have recently begun shipping millions of vaccine doses to COVAX, the UN-backed mechanism for equalizing access to COVID-19 vaccines.

“There’s still a market for the Chinese vaccines…simply because Western vaccines cannot meet the global demand right now,” says Huang.