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Spot the difference

The US measles outbreak highlights why most states should reconsider their vaccination rules.

Over the past decade, increasing numbers of US parents have chosen not to vaccinate their children against diseases such as whooping cough, mumps and measles. The consequence has been a periodic return of these historical scourges, in localized outbreaks of a few dozen to a few hundred people. These episodes often appear in local news reports, some of which warn that lower vaccination rates could result in a nationwide outbreak.

Reading the US news media over the past two weeks, you might conclude that that day has come. The current US measles outbreak, which began in December and was first reported in late January, has blown up into a national debate over the rights of parents to decide whether their children should be vaccinated. But by global standards, it is a tempest in a teapot: as of 6 February, measles had struck 121 people in 17 states and the District of Columbia.

Those numbers are unremarkable. Since October, a measles outbreak has affected more than 370 people in Germany; it saw almost 1,800 cases in 2013 and more than 1,600 in 2011. The Philippines had more than 50,000 cases in 2014. The United Kingdom had only 137 cases last year, but in both 2012 and 2013 it had close to 2,000 (see page 148).

In fact, even by US standards, the current outbreak is not unprecedented. Last year, a much larger outbreak was sparked by Amish missionaries returning from the Philippines to Ohio, where low vaccination rates among the community caused 383 cases.

Perhaps that incident stayed out of the national spotlight because it was an unusual set of circumstances that occurred in an isolated rural community. But the current outbreak centres on ‘the happiest place on Earth’ — Disneyland in southern California. At least 42 people seem to have been exposed to measles at the theme park, which receives an estimated 16 million visits a year.

Fortunately for the public’s health, attention around the outbreak has come down in favour of vaccination and against the myths about its dangers. Public opinion has turned against parents and physicians who are suspicious of vaccines. Two potential Republican presidential candidates, Governor Chris Christie of New Jersey and Senator Rand Paul of Kentucky, at first declared that parents should have the right to decide whether their children are vaccinated, and then had to clarify their positions in the face of harsh criticism.

Disneyland is at the epicentre of the US anti-vaccine movement.

Whether or not the theme park’s involvement in the episode contributed to the media coverage, Disneyland’s cherished place in US culture makes it ideal for an infectious-disease outbreak. It is popular with international tourists eager for a quintessential American experience, who as a group are less likely than US residents to be vaccinated. The park also hosts large numbers of infants less than one year old — younger than the age at which the first measles shot is generally given in the United States.

And Disneyland is at the epicentre of the US anti-vaccine movement. Although 94.7% of US children entering school at around age 5 are vaccinated against measles, in hundreds of California schools the percentage of vaccinated children falls well short of the 92% considered necessary to produce the ‘herd immunity’ that prevents transmission of the disease. The state’s public-health department reports that 2.54% of children entered school in 2014 with an exemption from vaccination based on personal belief.

The federal government has little say in who gets a measles shot — those rules are written by individual states. Most, like California, allow parents to send their children to school unvaccinated by claiming a religious or philosophical objection to the practice. But two — Mississippi and West Virginia — allow only medical exceptions. And that, many observers have argued, is why Mississippi, one of the poorest states in the union, has the highest percentage of 5-year-old children who have received vaccination for measles, mumps and rubella.

Last month, the Mississippi state legislature was considering a bill to allow the same types of personal-belief exemption that most other states allow. But on 3 February, a committee in the state’s House of Representatives killed the proposal. On 4 February, legislators in California said that they would introduce a bill to adopt the same strict rules as Mississippi. And several other states, including Maine, Minnesota and Oregon, are considering measures that would require parents to consult with a physician about vaccines before being granted an exemption.

That is a step in the right direction. Parents, of course, have the right to decide what is best for their children. But when it comes to vaccination, those decisions should be based on complete and accurate information about the risks and benefits.

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Measles by the numbers: A race to eradication 2015-Feb-11

Hidden bonus from vaccination 2014-Aug-06

Measles returns to Britain 2003-Aug-08

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Spot the difference. Nature 518, 137–138 (2015). https://doi.org/10.1038/518137b

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