Minnesota is in the midst of its largest measles outbreak in nearly 30 years with around 60 confirmed cases since April.

It’s being blamed on the spread of inaccurate information about the risks of vaccines - particularly among the local Somali community. The Minnesota Department of Health said in April that the group had been directly targeted:

“This outbreak is about unvaccinated children, not specific communities,” said the state’s Health Commissioner Dr. Ed Ehlinger. “Unfortunately, the Minnesota Somali community has been targeted with misinformation about vaccine risks.”

Anti-vac attitudes

In recent years, negative attitudes to vaccines have increased across the world, with the MMR (measles, mumps and rubella) vaccine coming under particular scrutiny.

A discredited 1998 paper linked the vaccine to autism. The report’s author was Andrew Wakefield, a British doctor who was later struck off the medical register in the UK for professional misconduct.

The Washington Post reports that the anti-vaccine movement gained traction among Somali parents after concerns in 2008 that autism was particularly prevalent in the community.

Although a study found these children were about as likely as white children to be identified as autistic, parents anxious to know more came across anti-vac attitudes online - including the disproven link to autism. Anti-vaccine activists - including Mr Wakefield - were reportedly invited to visit and speak with the community in Minnesota several times.

They have defended their role to the Washington Post, saying they were simply providing information.

Vaccination levels have plummeted in the community, falling from 92% in 2004 to just 42% 10 years later. To protect everyone from a measles outbreak, so-called herd immunity is needed - 83-94% of people need to be immunized against the disease.

Image: Vox

Measles in the US

Measles was eliminated in the US by the turn of this century, with any cases in the country brought in from abroad.

 Measles cases in the US, 1962-2011
Image: CDC

However, the disease is highly contagious. If they’re not immune, 90% of people in close contact with an infected person will be infected, according to the Centers for Disease Control and Prevention.

Cases therefore spread rapidly between people who haven’t been vaccinated, with Minnesota not the only place to experience an outbreak. In 2015, an outbreak in California was linked to Disneyland and in 2013 there was another one in Texas.

Concerns about vaccine safety in the US are among the highest in the world, as this map from Scientific American highlights:

Image: Scientific American

The US outbreak is not the only one linked to anti-vac attitudes, with recent cases in Italy and Romania also being partly blamed on a rise in parents refusing to vaccinate their children.

Measles around the globe

Measles deaths have fallen significantly in recent years - from more than half a million in 2000 to less than a quarter of a million in 2013.

But, around the world more than 20 million contract the disease every year, and it’s still common in many developing countries.

The most effective strategy to reduce cases, and deaths, is vaccination say the WHO. However, immunization levels remain lowest in low-income countries. Even in many developed nations, though, the herd immunity threshold has not been met.

Image: The Economist

As of 2014, 85% of one-year-olds around the world had been immunized.