He is of course correct.
Humans have concentrated themselves closely in cities having populations greater than 10 million very densely packed people. American and European cities might not have the density as say Indonesia or India or especially, China.
Java, a single Indonesian island has a population greater than all of Russia. Mumbai has people literally living in slums packed so close together it seems there is nothing there but people and especially children
It seems that some hybrid small pox or typhoid or cholera or many many other diseases could attack these dense populations and millions would die simply because governments have no defense other than let them play out.
America is susceptable in the squatter camps that are thriving in California and Washington. I seriously doubt that even though the cities have state of the art public health capabilities a real epidemic could be stopped early on
It’s not the natural pathogens that people are afraid of. Why do we need to develop unnatural pathogens and then create vaccines before the unnatural pathogens are released?