You’ve almost certainly seen the headlines. Measles, a serious and highly contagious disease that once seemed to be eradicated, is back with a vengeance.

Cases in Australia have hit a five-year high. Globally, there are outbreaks in the Philippines, Georgia, Thailand, Ukraine and the United States.

New York City has declared a public emergency to halt a measles outbreak, and Rockland County has tried to bar unvaccinated children from public places.

What is measles, anyway?

“It’s about the most infectious virus there is,” says Dr Mike Catton. About 90 per cent of unvaccinated people who come into contact with measles will catch it – it can live in the air for up to two hours.

Unvaccinated children are most at risk. Viruses tend to circulate a lot among them, their hygiene is not great, and generally their immune systems are weaker than adults', says Dr Catton, director of the Victorian Infectious Diseases Reference Laboratory.

Women who contract measles when pregnant are also at risk of pre-term labour, various complications and neonatal death.

In most cases, measles is uncomfortable but not life-threatening. Symptoms include a rash, which usually lasts three to five days, plus fever, cough and watery eyes.

About 60 per cent of people recover well but, in the other 40 per cent, measles can cause complications.

About 10 per cent of measles victims will suffer a severe complication that can include blindness, pneumonia, ear infections and swelling of the brain, which can be fatal.

For every 1000 children who get measles, one or two will die.

What’s happening? Is it back?

Yes. A concerted global health effort pushed measles to the brink of eradication in many countries, leading to an 80 per cent reduction in measles deaths between 2010 and 2017.

But the job was never quite finished. There were enough pockets of unvaccinated people for the disease to survive.

We dropped our guard.

On Tuesday, the World Health Organisation announced that worldwide measles cases had risen 300 per cent in the first three months of 2019, following two years of continuous increases.

There are sizeable outbreaks in Democratic Republic of the Congo, Ethiopia, Georgia, Kazakhstan, Kyrgyzstan, Madagascar, Myanmar, Philippines, Sudan, Thailand and Ukraine, causing many deaths.

In many of these countries, vaccination levels are low.

“They are an accident waiting to happen,” says Dr Mike Catton of these countries, “and they are causing big outbreaks of measles cases. That’s not a scenario we’re going to see in Australia."

Then what’s causing the outbreak in Australia?

Our situation is not comparable to the rest of the world, experts say.

We have had 97 confirmed cases of measles so far this year, which puts us on track for our worst year since 2014, when there were 339 cases.

But compare that to the US, where they really do have problems. Already this year, they’ve had 555 cases. That's the second-worst number of cases since it claimed to have eliminated measles in 2000.

Like Australia, the US has high overall vaccination rates.

The problem there is that people who are unvaccinated tend to cluster in small communities often based on ethnicity or beliefs – Orthodox Jewish communities have been particularly hard hit. When measles gets into such a community, it can spread like wildfire.

Australia is in a similar situation. We have world-leading vaccine coverage, high enough to confer herd immunity, and no circulating measles strains.

Our cases of measles are all caused by infected travellers coming to Australia, says Dr Catton, and then spreading it into small pockets of under-vaccinated people.

The global outbreaks mean Australian travellers are at higher risk of exposure, and of bringing the disease back and passing it on. That's what is causing the increase in numbers.

“It’s like a bushfire, with ember attack coming in and seeding sparks on your roof. They are peppering Australia with measles. Sooner or later, because it’s such an infectious virus, someone will get exposed,” says Dr Catton.

Can I blame the anti-vaxxers, such as Anthony Mundine?

Boxer Anthony Mundine recently took to Twitter to encourage his followers not to let “the government bully you into vaccine” – earning him condemnation from Australia's scientists – before he toned down his comments, saying he was simply for “informed consent and freedom of choice”.

But while there certainly seems to be a lot of anti-vax sentiment floating around, the anti-vax message does not seem to be having any impact on community vaccination rates.

“We have not seen it impacting on our vaccine rates as much as everyone has feared in Australia. That's encouraging,” says Dr Lucy Deng from the National Centre for Immunisation Research and Surveillance.

People who don't get vaccinated tend to be “at either end of the socio-economic spectrum,” says Professor Julie Leask, a University of Sydney academic who studies vaccine uptake.

The people who are most at risk of missing out on vaccines are not wealthy anti-vaxxers, they are the poor.

“The data shows that if there are more than two kids in the family, they are much more likely to be undervaccinated. That is a bigger group than the vaccine-refusers.”

Anti-vax sentiment does not appear to have increased in Australia, although anti-vaxxers have become increasingly “radicalised”, her research shows.

Am I protected?

If you were born between 1966 and 1992, you might not be as well protected as you could be.

Children born in those years were given a single dose of the vaccine. But scientists later learnt that, for the best coverage, you need a boost so children born after 1992 would have received two jabs.

One jab gives you a 90 per cent chance of being immune; two jabs boosts that to about 97 per cent.

That leaves millions of Australians with reduced protection, says Dr Deng.

You can check if you had one jab or two on your childhood immunisation records, if you still have them. If you received only one dose – or you're not sure – you can ask your GP for another shot.

If you were born before 1966, you may well have been exposed to the virus and developed immunity from an infection.

If you have had measles you have lifelong immunity from catching a second bout.

And if you are in doubt, there is no harm in getting a second jab, says Dr Catton.

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