Canterbury District Health Board is on high alert for new measles cases after finding out an infected passenger caught two domestic flights
Travellers on board two Jetstar flights between Christchurch and Auckland last week may have been exposed.
The infected person had been told to stay at home.
"They had been asked to keep themselves isolated and they, thereafter, got on a flight and flew down to Christchurch against instructions," Canterbury Medical Officer of Health Alistair Humphrey told RNZ.
"They then developed symptoms so tracking back we were able to [find out] that, unfortunately, they were contagious while they were on the flight."
The DHB is advising anyone who travelled on JQ237 on June 6 and JQ236 on June 8 to check their measles immunisation - and stay home from work or school.
"They can return to work if they are still not unwell on Saturday, June 22," Dr Humphrey said.
"It's impossible to know how many people on the flight would have been vulnerable in that way. Obviously if people are fully vaccinated they are not at risk."
Anyone showing symptoms - including a dry cough, headache, runny nose, temperature or rash - should also stay away from their local practise and hospital.
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"In Canterbury you can call your own GP team after hours and be put through to a nurse who can provide advice at any time of day or night - or people from outside Canterbury and living elsewhere in New Zealand can call Healthline on 0800 611 116," the DHB said in a statement.
Measles has been making a comeback in recent years with the rise of the anti-vax movement, which the World Health Organization recently named one of the biggest threats to health worldwide.