The issue isn’t about any particular measure that China should or should not have taken (and indeed, whether any other country would or should have done the same) but rather that it is quite evident that China did not report on a known contagion and has since embarked on a case of disinformation about the origins of the virus. Even if there was no way to stop spread of the virus (likely) the forewarning about the severity of the disease to the World Health Organization would have given nations more lead time to make preparations.
I’m personally agnostic about the “lab leak” theory, and I don’t subscribe to any notions that there was any deliberate effort on the part of the PRC to propagate the pandemic (which has hurt China economically at least as bad as any other developed nation) but the reality is that in autocracies and especially dictatorships there is the immediate and reflexive response to dissemble and disinform the public because that is how they maintain control of the population. The Soviet Union tried to lie and cover up the explosion of Chernobyl Reactor #4 (and didn’t reveal details of the partial meltdown in Reactor #1 and the other issues with #3 and #4 as far back as 1984), which wasn’t revealed until nuclear energy authorities in Sweden detected plume residues.
Of course, democracies also have coverups (especially those with agencies dedicated to clandestine operations and limited oversight) but they also have independent press that serves as an outlet for whistleblowers instead of just state-controlled media reporting pravda.
Stranger