Measles will likely spread to the South Island following outbreaks in Auckland and Hamilton, and Nelson families are urged to check they are immunised before the school holidays.
More than 200 cases of the highly infectious virus have been recorded since December,with most in children and teenagers aged 10 to 19 in the Waikato region.
Medical Officer of Health for Nelson and Marlborough Ed Kiddle issued a warning about the infectiousness of the virus to try to prevent measles getting established in the region.
Schools and preschools were asked to circulate the letter to students and parents, and ensure they had had the requisite two immunisations against measles, mumps and rubella, to have the highest level of protection against it.
Medical practices were also encouraged to check their records and to call in anyone who had not had two MMR vaccinations.
"The general level of immunisation you've got to have to give protection to a community is in the order of 95 per cent [of people vaccinated], so the closer we get to that figure the better, really," Kiddle said.
There had been no reported cases in the South Island following the outbreak, but the risk of the virus making it across the Cook Strait increased with the upcoming school holidays, Kiddle said.
"All you need is an unimmunised child to travel to the North Island and be exposed to measles and come back and bring it down here and if there's a pool of susceptible people here, they'd be at risk. So we want to try and avoid that."
Schools were targeted by the message because of the high rate of teenagers and young adults affected in the North Island outbreak, Kiddle said.
Most who got measles were not immunised or had only one MMR vaccination, and to be counted as fully immunised people needed two vaccinations after the age of 1.
There had been 14 suspected cases of measles in the region notified to the DHB this year, which had been followed up and tested, and none had been confirmed as measles.
The region's last confirmed case was in 2009.
Associate Health Minister Jo Goodhew also urged families to make sure they were vaccinated before heading away for the school holidays, as measles was highly preventable with immunisation.
The immunisation took 10 to 14 days to take effect, so there was still time to get the whole family vaccinated before the break, Goodhew said.
- The Nelson Mail
Does Nelson deserve to be classed as a city?Related story: (See story)