The Taranaki District Health Board is on high alert after confirmation a 15-month-old boy contracted measles overseas and brought it home this month.
The boy and his parents travelled from India on 1 November, made connecting flights in Asia, and arrived in Auckland the next day, before heading to Taranaki.
DHB chief medical adviser Greg Simmons said the child would have been infectious during the flights and when he returned home.
He said staff were working through a long list of people with whom the child had been in contact, to ensure they understood the symptoms and the risks of measles.
"There have been a number of health settings where the child has exposed other people and those people have varying levels of risk depending on whether they've been immunised or not and depending on their age."