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Explainer: Measles cases may be spreading in the community. Here’s what you need to know about the deadly disease.

Measles cases have been breaking out around Aotearoa in recent months, with Health NZ's public health medicine specialist Dr Sharon Sime warning there may be undetected cases circulating not linked to overseas travel.

Measles is highly contagious - up to 90 percent of non-immune people (those who have not been vaccinated or have not already had it) will be infected if they are exposed to the virus.

The measles vaccine is free, delivered as part of the MMR vaccine (measles, mumps and rubella).

About 80 percent of New Zealanders are immune - well below the 95 percent coverage needed to prevent an outbreak - and it is lower still for young children, who are among those most at risk of serious complications.

Just 76.4 percent of two-year-olds were fully vaccinated as of December 2024. The rates were worse for Māori babies (63.3 percent) and Pacific (70.4 percent).

Here’s what you need to know.

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What is measles?

Measles is one of the most infectious diseases known, infecting children as well as adults via coughing, sneezing or talking. It is not known to affect any other species.

People who come into contact with the disease who are not immune through vaccination or previous infection are about 90 percent likely to become infected.

Before vaccines, 90 percent of people over 20 had been infected at some point in their lives.

About one in 10 people who contracts measles need hospital treatment. The virus can live in the air for hours after a person has been coughing and sneezing in the area.

Symptoms include fever, coughing, having a runny nose and wate