Why measles might still get you, even if you're vaccinated

Millennials and Generation X are being urged to get booster measles vaccination shots, as the Canterbury outbreak spreads.

Twenty-two people are now confirmed to have been infected.

"Measles should be eliminated from New Zealand," University of Auckland infectious disease specialist Emma Best told The AM Show on Monday.

"We haven't had many cases for several years - we've now got a big cluster of cases in Canterbury. We don't have measles transmission normally happening in New Zealand, it's a disease that should be gone."

Every measles outbreak in New Zealand nowadays begins when someone carrying the virus arrives from overseas. But thanks to high levels of vaccination and 'herd immunity', the virus - despite being one of the most infectious on Earth - has trouble spreading.

The World Health Organization recently named 'vaccine hesitancy' as one of the biggest threats the world faces. But the current outbreak can't be entirely blamed on anti-vaxxers - even some people who have got the vaccine aren't immune.

"We know that some people when we first started vaccinating were receiving one dose - and actually, we know that we need two doses to be properly immune. That's why there's a gap in immunity."

Emma Best.
Emma Best. Photo credit: The AM Show

Nowadays kids get their first dose at 15 months and the second at four years - but this regime only began in 1992. Before 1969, measles was rampant - so anyone around before then is considered probably immune.

It's the group born in between those two dates that are at risk.

"We gave one vaccine through the '70s, '80s and '90s - so there's a bunch of people in their 20s, 30s and 40s who actually may have only had a single dose," said Dr Best.

The good news is it's perfectly safe to get another dose if you didn't get the second one, or you're not sure.

"There is absolutely no harm in going to your doctor and saying, 'I need a second dose.'"

If you suspect you've been infected, Dr Best says it's important you call a doctor or emergency department first - don't go in, or you risk spreading the "nasty" illness.

"A fever, a rash that spreads from behind the ears, down over the whole body. Complications as well - measles can cause pneumonia, measles can cause brain inflammation, encephalitis. It can cause you severe harm, as well as death."

Because of the virus' lengthy incubation time, it could be another month before New Zealand is measles-free again - that's if it doesn't continue to spread.

Measles used to kill several hundred people a year, according to Te Ara: The Encyclopedia of New Zealand. More than 500 died in 1893.

As recently as 1997 there was a major outbreak which saw hundreds hospitalised.