With the traffic on and off the island, I'd imagine the modern native population has a much higher resistance to Asian and European pathogens than even a generation ago.
The article didn't go into details, but there was originally much contact between Ni'ihau and the other islands, though mostly the nearest, which is Kaua'i. During the period of initial contact with Westerners, many Hawaiians on all islands did die of Western diseases, but their population did survive. It's only in the past hundred years that Ni'ihau has been mostly cut off--though the owners and residents do come and go and mingle with the general population on Kaua'i. And nor have they been cut off from Western medicine, so I imagine they are all vaccinated like everyone.
Still, it is an interesting question whether this semi-isolated population has some lingering susceptibility to certain diseases.
