Tiana Allen said her 10-month-old son Isaiah was exposed to measles at Waikato Hospital.

Several more people are under investigation for measles in the recent outbreak in the Waikato.

There are now 11 confirmed cases of measles and another 11 people suspected of having measles.

Of the 10 confirmed cases, two attended a kapa haka festival at Claudelands Event Centre in Hamilton on Saturday, April 16. More than 5000 people attended the event.

One confirmed case is a Waikato District Health Board staffer.

And of the 11 cases under investigation by the Waikato District Health Board, four attended the festival and the other seven had links to another infected person.

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Waikato DHB medical officer of health Felicity Dumble said at least five of the suspected cases attended the emergency department between March 25 and April 19. Three were admitted to hospital.

Hamilton mum Tiana Allen was at the Waikato Hopsital emergency department on April 24 with her 10-month-old son, Isaiah. She was told by a nurse that her son shouldn't be at the hospital as there were children in the play area suspected of having measles.

Allen is keeping an eye on her son for symptoms, as measles has an incubation period of two weeks. Isaiah is too young to have been immunised, a jab usually given at 15 months.

During an outbreak in 2014, there were 125 measles cases in Hamilton. Four of those were considered fully immunised.

Two doses of MMR (measles, mumps and rubella vaccine) provides 95 to 98 per cent immunity.

"People should ring ahead and warn us if they are coming to hospital so we can prepare for that, or they can call their GP or Healthline for advice," Dumble said.

Dumble said when an outbreak occurs, the DHB will urge parents to vaccinate earlier than the usual age of 15 months. Children can be vaccinated from the age of six months but will still need to get another dose at 15 months and then again at four years.

Measles is spread by tiny droplets in the air and is one of the few diseases that can spread easily to those nearby.

Symptoms don't appear for at least two weeks after exposure. The first symptoms are fever, runny nose, cough and sore, runny eyes. The rash starts later.

If people do not have immunity, they should be vaccinated as soon as possible. People could also call Healthline on 0800 611 116 for advice or seek medical attention depending on the severity of illness.