BEIJING -- Gao Fu, head of the Chinese Center for Disease Control and Prevention, said he had received three doses of Chinese COVID-19 vaccines, each of which was different in type and manufacturer, and felt no discomfort, Singapore's Lianhe Zaobao reported Wednesday.

Gao explained that he did this out of confidence in the country's vaccines.

In regard to the vaccines' validity period, Gao said there is no definite answer at present, as this is the first time for humans to develop coronavirus vaccines, and many things remain unknown.