Densely populated areas are vulnerable to dangerous outbreaks of infection such as measles – and to the spread of misinformation

Just a 30-minute drive from Portland, Oregon, is Washington’s Clark County, home to one of the largest outbreaks of measles in the US. Of the 70 or so confirmed cases, the majority are unvaccinated children under the age of 10.

In a country that had previously eliminated measles, in 2000, hundreds of children are being kept out of school to avoid exposure to the disease. It is so contagious that if one child is diagnosed, all are considered at risk.

The outbreak, declared a public health emergency earlier this year, began when an infected person from another country visited the area. All it took was for this “patient zero” to come into contact with children who hadn’t been inoculated. Then, as these children visited healthcare facilities, schools, churches and a furniture shop, the disease began to spread.

Facebook Twitter Pinterest A sign prohibiting all children under 12 and unvaccinated adults at the entrance to PeaceHealth Southwest Medical Center in Vancouver, Washington. Photograph: Gilliam Flaccus/AP

But why did the outbreak take place here rather than elsewhere in the country?

Some US states, including Oregon and neighbouring Washington, allow easy opt-outs for vaccines, allowing parents to skip immunisation if they express a personal objection. Last year, research published in the journal Plos Medicine found “hotspots” of “anti-vaccine activity” in the 17 states that allow exemptions on the grounds of personal belief – affecting the cities of Seattle, Portland, Phoenix, Salt Lake City and Austin in particular.

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“We identified about a dozen cities where there are large numbers of children who are not receiving their vaccines because their parent opted them out of vaccination for non-medical reasons,” says study co-author Peter Hotez, professor at Baylor College of Medicine.

“The common denominator of most of these hotspot urban areas is that they are targeted by the anti-vaccine lobby, which is well-organised and well-funded, with 480 anti-vax websites, social media and books.”

Living in a city means being in close proximity with millions of people every day, as you pass in apartment buildings, offices or on public transport. And while most of us have caught a cold at some point, we tend not to worry about catching something more serious like measles, especially if we were inoculated in childhood. After all, vaccines have helped to consign once-deadly outbreaks to history. Yet over the last decade diseases like measles, mumps and whooping cough, once disappearing, have made a resurgence.

This year, the World Health Organization declared the anti-vaccination movement a top 10 health threat, after a 30% rise in measles cases worldwide – including in countries where the virus had been virtually eliminated.

Facebook Twitter Pinterest People against mandatory vaccinations participate in the ‘March for Medical Freedom’ outside the Legislative Building in Olympia, the capital of Washington state. Photograph: Lindsey Wasson/Reuters

You can catch measles anywhere, but opportunities for infection are often strong in areas of high population. And given that by 2050 an estimated seven in 10 people will living in cities globally, public health is a pressing concern.

“Viruses spread easily in urban environments,” says Arthur Caplan, a professor of bioethics at New York University. “Plus cities are transportation hubs providing truck, car, train and plane routes for infected people to spread disease worldwide.

“The more unvaccinated people there are, especially in cities, the easier the spread of disease. Anti-vaxxers put their communities and others at risk. Many people and children and newborns can’t be vaccinated due to transplants, cancer treatments, immune diseases. You vaccinate to protect yourself and kids and neighbours who cannot.”

Cities are also constantly on the move, providing more opportunity for diseases to spread. “Cities often have more transient populations – with people coming and going and sometimes bringing infectious diseases with them which can spread among unvaccinated people,” says Heidi Larson, director of the Vaccine Confidence Project at the London School of Hygiene and Tropical Medicine. “Unvaccinated travellers can also contract infectious diseases from local populations and carry them to other places.”

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Vaccine resistance movements are as old as vaccines themselves, but misinformation was particularly fuelled when, in 1998, a now-retracted and debunked study by Dr Andrew Wakefield wrongly linked the measles, mumps and rubella jab with autism. In recent years, anti-vaccine sentiment has coincided with the proliferation of “fake news” and a general disregard for science.

Anti-vaxxers may be in the minority, but it doesn’t take much to undermine “community immunity”– a form of protection from disease when a large percentage of the population has become immune to an infection, protecting those who aren’t.

Around half of all parents with small children have been exposed to misinformation about vaccines on social media, a recent report by the Royal Society for Public Health found. “Cities more typically have higher media saturation and more opportunities for the spread of misinformation,” Larson says.

Facebook Twitter Pinterest Edward Jenner, pioneer of the smallpox vaccine, and two colleagues see off anti-vaccination opponents, with the dead littered at their feet. Coloured etching by Isaac Cruikshank, 1808. Photograph: Wellcome Library, London

Certain groups are more likely to harbour anti-vaccine views, although this is changing, says Dr Saad Omer, director of the Yale Institute for Global Health.

“We know that at least a few years ago, although it has slowly changed, vaccine refusal was often clustered in very urban, educated, large families,” he says. “But it’s not exclusive to that group now. Like other social phenomena, sometimes it starts in certain populations but it diffuses out.”

Highly contagious, the measles virus can live in the air or on a surface where an infected person has coughed or sneezed for up to two hours, infecting up to 14 others. And in crowded cities, children who are too young to be vaccinated are at particular risk.

Catherine Cooper was living in south London when her eight-month-old son Toby contracted the virus. It was 2003, a time when take-up of the measles vaccine was falling following Wakefield’s study.

The doctor spotted the “baby with the rash” and asked Cooper to jump the queue. “She asked if she could call in a newly qualified doctor from the next consulting room to show [Toby] to her, as it was likely she had never seen a measles case,” she says.

“He spent the week floppy and unhappy but recovered. He caught it in the creche of my local gym so I assume from an unvaccinated child – the creche catered for older children too.”

Measles outbreaks in the US and Europe have been declared emergencies, but experts warn the consequences of the anti-vaccination movement could be most acutely felt in lower-income countries. Preventable diseases are more likely to kill in densely populated cities with poorer healthcare infrastructure.

Facebook Twitter Pinterest Access to reliable, factual information about vaccine safety is a priority for public health bodies. Photograph: Brian Snyder/Reuters

“It is reasonable to have concern about cities, not just in the developed world, but also in the developing world,” says Omer. “There is a perception that vaccine refusal is a western concept, but it’s not. There was vaccine refusal during smallpox eradication. There is vaccine refusal for polio and measles in several parts of the world.”

And anti-vaccine sentiment poses a further risk when access to vaccines is still a problem in many cities, including in London, where immunisation rates for MMR (measles, mumps and rubella vaccine) are lower than the rest of the UK.

“This is due to a multitude of reasons: large mobile population who may change GPs frequently, pockets of severe disadvantage, people not registered with GPs,” says Helen Bedford, professor of child’s health at UCL.

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“The anti-vaccine movement may threaten people if they influence those who are undecided about vaccination, who perhaps have concerns about vaccine safety but do not have access to health professionals who are important for allaying fears and discussing concerns.”

For example, the 2017 measles outbreak in Minnesota – the largest in the state for 30 years – was largely ascribed to anti-vaccination misinformation specifically aimed the Somali-American community in Minneapolis. Over 80% of the cases in Minnesota involved unvaccinated Somali-American children, showing exactly the impact such messaging can have.

And with our cities continuing to expand, improving vaccine coverage – and access to reliable, factual information about vaccine safety – needs to be a priority for public health bodies.

“Science has demonstrated repeatedly that vaccines are highly effective and very safe,” Bedford says. “We need parents and celebrities, as well as scientists being more vocal about the value of vaccines. We can use social media and stories of individuals damaged by diseases can be very powerful. These are the tactics used by anti-vaccine groups – we should be employing them too.”

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