HONG KONG – In a surprisingly candid statement, the director of China’s Centers for Disease Control (CDC) conceded that the efficacy of Chinese coronavirus vaccines is "not high" and may require improvements.

George Gao, the director of China’s CDC, stated that Chinese vaccines “don’t have very high protection rates” at the National Vaccines and Health conference in the southwestern city of Chengdu on Saturday.

Though it has recorded better efficacy numbers in Indonesia and Turkey, Sinovac Biotech Ltd.’s vaccine was found to have an efficacy rate as low as 50.4% in phase III trials in Brazil.

Ahead of peer review, Brazilian researchers had also found two injections of the vaccine was 49.1% effective when given shorter than three weeks apart, lower than the 50% bar set by the World Health Organization.

However, studies on a small subgroup showed that the efficacy rate increased to 62.3% when the doses were given at intervals of three weeks and longer.

This is a particularly large gap given that other vaccine developers, such as Pfizer Inc. and Biontech SE, for example, recorded 97% efficacy against symptomatic coronavirus in an Israeli study.

China has yet to approve any foreign vaccines on its home turf. So all of the doses adminstered would have been from domestic manufacturers like Sinovac and Sinopharm. So far, more than 34 million people have received the two doses required by the Chinese vaccines and roughly 65 million people have received one, according to Gao.

At the conference, Gao revealed that Chinese authorities were considering using different types of vaccines.

Varying solutions proposed

“It’s now under formal consideration whether we should use different vaccines from different technical lines for the immunization process,” said Gao.

He suggested changing the number of doses and the length of time between doses as a solution to efficacy issues.

"The protection rates of all vaccines in the world are sometimes high and sometimes low. How to improve their efficacy is a question that needs to be considered by scientists around the world," Gao told state media.

"In this regard, I suggest that we can consider adjusting the vaccination process, such as the number of doses and intervals and adopting sequential vaccination with different types of vaccines."

Switching strategies might work if a correct approach is adopted.

“Switching up inactivated vaccines, such as Sinovac and Sinopharm’s vaccines, won’t do much as they are based on similar technologies,” Benjamin Cowling, head of the University of Hong Kong’s (HKU) epidemiology and biostatistics division, told BioWorld.

But he said switching up the dosage amount and time between doses might help.

“By accident, the Astrazeneca vaccine was administered at half the usual dosage for first dose, and full for the second dose in their UK study. It’s fascinating that the inadvertent dosing led to a higher efficacy rate. That could be worth exploring in studies,” said Cowling.

It was also found that having a 12-week interval between doses, instead of the six-week interval, led to higher efficacy rates of 81% and 55% respectively for the Astrazeneca vaccine.

China also has a number of mRNA vaccine candidate in the works.

Cowling suggested that should China adopt a dose sparing strategy, the scientifically sound way would be to do the mRNA vaccine for the first dose, followed by an inactivated vaccine for the second.

“The order would matter because the mRNA vaccine tells the immune system how to react and then the inactivated vaccine boosts the memory of the protein in the second shot,” he said.

“Those that received the Sinovac and Sinopharm vaccines can look into maybe getting a booster shot in six to 12 months. But it wouldn't be right to assume a higher level of protection, there needs to be a study establish the efficacy first,” he stressed.