https://www.bbc.com/future/article/20181023-the-places-that-escaped-the-spanish-flu
The places that escaped the Spanish flu
In Denmark, for example, the pandemic claimed just 0.2% of the population while in Australia just 0.3% died. China also escaped lightly, with relatively few deaths – again something that has been attributed to some existing immunity within the population. Some large cities also reported lower mortality rates than might be expected in places where the risk of passing the virus from person to person is high, perhaps also due to immunity obtained in earlier less deadly outbreaks.