Did places like the Pitcairn Islands escape this flu? Any other places?
Google is your friend!
The places that escaped the Spanish flu
The pandemic killed “just” 0.2% Denmark,and 0.3% in Australia. China seems to have been barely affected. There were also isolated communities in the US which were unaffected, possibly unaware. American Samoa had no fatalities while it was 20% in neighbouring Western Samoa
Australia was very lucky its ports being more than 3-4 days sail (the incubation period of influenza) from anywhere else, so most ships that could have been carrying the flu were spotted before they landed.
Also, the nation had federated 18 years previously, and one of the strongest arguments for the colonies coming together was to enforce consistent maritime quarantine. As a result it had invested in a bright shiny new national quarantine network that was just waiting for a pandemic to happen.
You can see all this at the gob-smackingly fantastic North Head Quarantine Station in Sydney.
The link describes a place in Colorado, Gunnison, which shut off access to the world and escaped the flu. It helps to be small and remote - and self sufficient.
There’s a good article (text or audio) all about the spread of it here at Hakai magazine.
Not only that: people reacted with all the maturity and informed common sense that you see on display now in relation to NC19 
Returning soldiers nearly rioted when, after being on board and in quarantine for the last month, they were held off shore and in quarantine for another week…