When New Jersey Governor Chris Christie arrived in Britain this week he hoped to burnish his image as a 2016 presidential candidate. Instead, he was embroiled in a growing United States controversy that exposes his party's sceptical relationship with science.
The issue at hand was vaccinations; specifically if Americans should immunise themselves against measles, a highly infectious airborne virus making a strong US comeback.
The nationwide outbreak began in December, traced to the Disneyland theme park in Anaheim, California. The Centres for Disease Control says 105 people have been infected, with most cases in California. The outbreak follows a "record number" of measles cases last year and is stoking public unease, a test for Republicans seeking to entice their conservative base - viscerally suspicious of science - while presenting themselves as fit to rule.
Initially, Christie favoured "balance". Parents should decide if children needed to be vaccinated (his children had measles shots), as "not every disease is as great a public health threat as others".
Politically, this seemed smart, genuflecting towards his party's belief in individual choice and disdain for "big government". But as measles cases mounted, the "anti-vaxxers" - an often well-to-do, bipartisan movement - found themselves pilloried across the US for incubating a virus that put wider society at risk.
Christie, who had publicly disagreed with Barack Obama - the President urged parents to get their children immunised - soon had second thoughts, declaring that "with a disease like measles there is no question kids should be vaccinated".
The Governor's initial response, praising choice, clashed with his 2014 stance towards Ebola when - like many Republicans - he demanded draconian Government sanctions of US healthcare workers who had been in the West African hot zone, insisting they be quarantined.
As politicians bickered the CDC, mindful France went from 40 to 10,000 cases in 12 months [the 2008-2011 outbreak infected 20,000], urged Americans to vaccinate. While measles was eliminated from the US in 2000, the virus can be reintroduced and there are fears it may again become endemic. A 2014 outbreak infected 644 Americans in 27 states, the worst measles flare-up in 20 years.
The genotype from that outbreak matched the B3 virus found in 14 other outbreaks in 2014, such as one in the Philippines that infected over 50,000. They included Amish missionaries, volunteering in the aftermath of Typhoon Haiyan, who infected 383 at home in Ohio. Many Amish had eschewed vaccinations.
"This was a significant problem," says Dr Raymond Strikas, from the CDC's National Immunisation Programme.
"Measles was introduced to a population that was largely susceptible and therefore got sick. That's the challenge we have."
It is especially galling to the CDC that a MMR [measles, mumps, rubella] vaccine has existed since 1963. Before that measles infected about 4 million Americans annually, killing 500. The current US death rate is about 2 in 1000, with most victims dying from complications such as pneumonia or encephalitis (swelling of the brain).
While the MMR vaccine uptake is over 90 per cent nationwide, non-vaccinated pockets, where the disease can find a beachhead, have opt-out rates of 20 to 30 per cent.
Once measles gets a hold it is tenacious, as the French and Philippines outbreaks show.
In the developing world measles is a scourge of the impoverished, especially malnourished children in war zones and among refugee populations. The virus infects 20 million worldwide and in 2013 killed an estimated 145,700 (New Zealand had 283 cases in the year to November 2014).
Yet far away from such misery, where aid workers are often prevented from immunising children by armed groups, such as the Taliban, a "wealthy world epidemic" is emerging.
It is perhaps no surprise the present US outbreak started in California, epicentre of America's anti-vaccine movement.
"The resistance to vaccination, particularly in wealthy and upper-class communities, is really at the crux of the problem," says Laurie Garrett, a senior fellow at the Council on Foreign Relations and Pulitzer Prize-winning science journalist.
The Hollywood Reporter found some elite schools in Beverly Hills and Santa Monica had vaccination rates "as low as Chad or South Sudan's".
Despite assurances by California's public health officials that MMR is "more than 99 per cent effective in preventing measles", many anti-vaxxers use a "personal belief exemption" [PBE] to avoid immunising their children.
Records show a steady rise in unvaccinated kindergartners, from 0.77 per cent in 2000, to 3.15 per cent in 2013. At some schools the PBE rate is much higher, up to 75 per cent, as wealthy areas suffer from a marked upswing of pertussis, or whooping cough, and measles, both preventable.
Some parents want to raise children in a natural, organic way, rejecting the notion of fighting pathogens by injecting them into the body. Others have religious objections. Still others distrust pharmaceutical companies or fear vaccines may promote neurological and anti-immune disorders, a belief fanned by a retracted 1998 Lancet claim that linked vaccines with autism.
This development is emerging in tandem with another major trend, says Garrett, as wealthier Americans place their children in charter or private schools, which are far more tolerant towards non-vaccinations than the public school system.
Ironically, the anti-vaccine movement is cushioned by medical breakthroughs; many adherents are too young to remember the pre-vaccine era, when now preventable diseases like polio stalked the West.
While health officials worry that rich pockets of anti-vaccine followers are catalysts for the measles outbreak, poor neighbourhoods pose far less of a threat. After an uptick of diseases in the Reagan era, which rolled back public spending, the Clinton and Bush Administrations aggressively pursued federal immunisation programmes, making vaccination almost free for poor families.
Some states made it incumbent for parents to vaccinate children if they wanted to attend public schools. Mississippi, America's poorest state, has a 99 per cent vaccination rate. California, one of the richest states, has a vaccination rate in some counties of 88 to 89 per cent.
"The big change is that it's the relatively wealthy who choose not to vaccinate," says Garrett, a trend documented on an interactive map on the Centre for Foreign Relations website. "It's no longer to do with poverty."
Those in the anti-vaccine camp insist their choice is personal - they take the risk, if any. Garrett debunks this, insisting opting out is a false choice that endangers society as well as unvaccinated children, who must survive in a virus-ridden world.
"It's a choice that reflects a complete lack of solidarity with the rest of global society."
The belief that individuals supersede society, Thatcherism's most infamous tenet, has grave implications for public health when lethal pathogens, like Ebola, can exploit globalisation.
Of course, viruses do not discriminate between rich and poor.
They strike down the vulnerable.
Garrett, whose 1994 book The Coming Plague has proven prescient, fears libertarians may undermine the US public health system, even as anti-vaxxers unwittingly create opportunities for diseases. The 2014 Ebola outbreak in West Africa found the United Nations on the back foot, slow to respond, a failure that drove up the death toll, now at 8981. Last month, World Bank president, Jim Yong Kim, warned the world is "dangerously unprepared" for a pandemic. Opting out is no defence.
• Measles is a highly contagious viral disease affecting mostly children. It is one of the leading causes of death among children even though a safe and cost-effective vaccine is available.
• More than 95 per cent of measles deaths occur in low-income countries with weak health infrastructures.
• More than 145,000 people died of measles in 2013, 122,000 in 2012.
• In 2013, more than 70 per cent of global measles deaths were in six countries - India, Nigeria, Pakistan, Ethiopia, Indonesia and the Democratic Republic of Congo.