BEIJING (AP) – China’s top disease control official said in a rare appreciation that current vaccines offer poor protection against the coronavirus and that mixing these vaccines is one of the strategies being considered to increase their effectiveness.

China has distributed hundreds of millions of doses of domestically manufactured vaccines overseas and relies on them in its own mass vaccination campaign.

However, the director of the Chinese Center for Disease Control and Prevention Gao Fu said at a conference on Saturday that their effectiveness rates needed to be improved.

“We will solve the problem that current vaccines do not have very high protection rates,” Gao said in a presentation on Chinese COVID-19 vaccines and vaccination strategies at a conference in southwestern Chengdu. “We are currently looking into whether we should use different vaccines from different technical fields for the immunization process.”

He also praised the benefits of mRNA vaccines, the technology behind two of the most widely recognized vaccines, Pfizer-BioNTech and Moderna, months after asking if the untested method was safe.

In a message to The Associated Press late Sunday evening, Gao said he was speaking about efficacy rates for “vaccines in the world, not specifically for China.” He did not answer any further questions about the vaccines he was referring to.

He referred the AP to an interview with the state-run Global Times, which published several articles that cast doubts about the safety of Pfizer’s mRNA vaccine. Gao was quoted by the point of sale on Sunday as saying that he had been misunderstood and was simply talking broadly about improving the vaccine’s effectiveness.

Beijing previously tried to cast doubt on the effectiveness of the Pfizer BioNTech vaccine, which uses the genetic code known as messenger RNA, or mRNA, to boost the immune system.

Health officials at a press conference on Sunday did not directly respond to questions about Gao’s comment or possible changes to official plans. However, another CDC official said Chinese developers are working on mRNA-based vaccines.

“The mRNA vaccines developed in our country have also entered the clinical trial phase,” said Wang Huaqing, official. He did not give a schedule for possible use.

Experts say mixing vaccines or sequential immunization could increase their effectiveness. Researchers in the UK are investigating a possible combination of Pfizer-BioNTech and the AstraZeneca vaccine.

Gao ended his presentation on Saturday with praise for mRNA vaccines and called for innovation in research.

“Everyone should consider the benefits mRNA vaccines can bring to humankind,” said Gao. “We have to follow them carefully and not ignore them just because we already have several types of vaccines.”

Gao previously questioned the safety of mRNA vaccines. He was quoted by the official Xinhua News Agency as saying that he could not rule out negative side effects in December as it was being used for the first time in healthy people and said, “There are safety concerns.”

Chinese state media and popular health and science blogs also questioned the safety and effectiveness of the Pfizer BioNTech vaccine, although large-scale studies and the introduction of the vaccines in the US have proven its safety.

China currently has five vaccines in use as part of its mass immunization campaign, three inactivated virus vaccines from Sinovac and Sinopharm, one one-shot vaccine from CanSino, and the last one from Gao’s team working with Anhui Zhifei Longcom.

According to the companies, the effectiveness of the vaccines is between a little more than 50% and 79%.

The shot by Gao’s team was approved for emergency use a month ago and has not yet publicly disclosed any data on its effectiveness.

Studies have shown that Pfizer and Moderna vaccines, which are mainly used in developed countries, have about 95% protection against COVID-19.

As of April 2, around 34 million people in China have received full two doses of Chinese vaccines, and about 65 million have received one, according to Gao.

Globally, public health experts have said that any vaccine that is 50% effective would be useful, and many governments have been eager to use Chinese vaccines as rich countries around the world have taken pictures of Pfizer and Moderna.

WHO director general Tedros Adhanom Ghebreysus said Friday that while one in four people in rich countries received a vaccine, only one in 500 people in poorer countries received a dose.

The coronavirus pandemic, first spotted in central China in late 2019, marks the first time the Chinese drug industry has played a role in responding to a global health emergency.

Vaccines from Sinovac, a privately held company, and Sinopharm, a state-owned company, make up the bulk of China’s vaccines, which are sold in several dozen countries, including Mexico, Turkey, Indonesia, Hungary, Brazil, and Turkey.

However, the companies have not released publicly peer-reviewed data on end-stage clinical trial research and have been criticized for a lack of transparency.

For example, Sinovac’s vaccine gave cause for concern when it was found to have different rates of effectiveness ranging from 50% to over 83% in each of the studies conducted in different countries.

A Sinovac spokesperson, Liu Peicheng, admitted varying levels of effectiveness were noted, but said it could be due to the age of the people in a study, the strain of the virus, and other factors.

Beijing has not yet approved foreign vaccines for use in mainland China.

Sinovac spokesman Liu said studies have shown that protection “may be better” if the time between vaccinations is longer than the current 14 days, but gave no indication that this could be made standard practice.

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Wu reported from Taipei.

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This story has been corrected to show that Chinese vaccines have been donated or exported to several dozen countries, not 22, and that Sinovac is a private, not state-owned company.