The head of China's Centers for Disease Control admitted that the efficacy of Chinese coronavirus vaccines is "not high" and they may require improvements, marking a rare admission from a government that has staked its international credibility on its doses.

The comments on Saturday from China CDC director George Gao comes after the government has already distributed hundreds of millions of doses to other countries, even though the rollout has been dogged by questions over why Chinese pharmaceutical firms have not released detailed clinical trial data about their efficacy.

China has struck deals to supply many of its allies and economic partners in the developing world and advertised the fact that world leaders from Indonesia to Pakistan to the United Arab Emirates have taken them.

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Now, China is “formally considering” options to change its vaccines to “solve the problem that the efficacy of the existing vaccines is not high,” Gao told a conference in Chengdu in remarks that quickly spread through Chinese social media on Saturday before being mostly censored. Soon people were intentionally misspelling words in their posts while discussing the comments to keep them from being removed.