Measles rate rises amid global outbreak but Australia's immunity remains high

https://www.theguardian.com/australia-news/2019/mar/31/measles-rate-rises-amid-global-outbreak-but-australias-immunity-remains-high

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A recent spate of measles infections is on track to make 2019 Australia’s second-highest year for measles reports since 1997.

However, Australia’s overall immunity remains high, experts have said, despite growing anti-vaccination sentiment.

On Tuesday Victorian health authorities issued a warning after a person with measles flew from Melbourne to Christchurch on 19 March. This was after an earlier incident when a woman attended the Moto GP while infectious. There have also been measles outbreaks in New Zealand, Japan and the US in recent months, and more than 200 people have died in the Philippines this year.

Australia eliminated endemic measles in 2014, meaning no Australian has been infected by another Australian since then because of a strong herd immunity from vaccination.

But infections still occur because of arrivals from overseas. The number has crept up in recent years due to growing anti-vaccination sentiment, increased travel and other factors, said epidemiologist Gideon Meyerowitz-Katz, of the Western Sydney local health district.

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In three months there have been eight cases of measles in Victoria and 77 nationwide. There were only 74 cases in 2015. On current trends, 2019 is on track to have 300 infections, a number not exceeded, apart from 2014, since 1997.

“But that’s not necessarily worrying,” Meyerowitz-Katz said. “The disease is all coming from overseas, and given our high vaccination rate it’s probably not going to spread. But it is not an ideal trend.

“Many cases are children who are immuno-compromised, or unvaccinated for some reason. They catch measles from someone they run into overseas.

“Measles is one of the most infectious diseases around. In a vulnerable population – people who haven’t had the disease before or who haven’t been infected – they will pass on the disease to 18 other people, on average. In comparison, something like rubella or mumps spreads to between four and seven people.”

The reduction in immunity levels is not all due to anti-vaccination belief.

The measles vaccine requires two doses to become maximally effective, and Australian health authorities have warned that many adults between 26 and 52 years old received only one.

Measles vaccination programs began in Australia in the 1960s, but it was not until 1992 that the second dose became routine. Currently children are given doses at 12 months and 18 months.

The measles vaccine is 93% effective with one dose, and 98% with two doses.

Meyerowitz-Katz said access to healthcare generally also contributed to patches of measles vulnerability.

“The main reason why people don’t get vaccinated, aside from anti-vaccination sentiment, is that the services aren’t available or free, or may be a six-hour drive from the town,” he said. “Sometimes small or very small towns can have low vaccination rates due to the nature of sparsely populated areas.

“Transient populations also have very low vaccination rates. People who don’t stay in one place long enough to see a doctor, that increases the rate of infection … Anti-vaccine sentiment is quite common in some places [but nationally] it’s not just anti-vax sentiment.

“The MMR [measles, mumps and rubella] vaccine is super safe and the Australian government offers it for free … The idea of vaccines like this is you reach a threshold of herd immunity, so that that small remainder of 2% don’t catch the disease.”

Developing nations have much higher rates of measles than Australia.

Victoria’s chief health officer, Brett Sutton, said on Thursday: “There is a lot of measles circulating in our region currently, including much of south-east and southern Asia. All travellers need to be aware of this risk.”