To be clear, what I think happened is that the Chinese authorities believed until very late (anytime between Jan 15 and Jan 20) that the virus could be fully contained and everything kept tightly under wraps. Perhaps they thought it had a low R0 (like SARS)

So it was critical for them to have the @WHO play along and minimize the tgreat in its public communications. This was probably arranged at the highest level. But everyone knew, already in December, that there was human transmission. It was happening daily in Wuhan

And of course there was a confirmed case in Thailand on January 13. Unless pangolins and bats had been traveling with Chinese tourists to Thailand. The next day the WHO infamously tweeted that studies showed no human transmission. But the Thai case helped shift mood in Beijing...