The outbreak was originally limited to Disneyland visitors / AP

Two potential candidates for a run at the White House have questioned the need for parents to give their children the MMR vaccine

The Republican Party is on the defensive after two of its leading presidential hopefuls indicated that they had sympathy for parents unwilling to vaccinate their children against infectious diseases, even in the midst of a dangerous outbreak of measles centred in California.

One day after both Senator Rand Paul and Governor Chris Christie publicly questioned the requirement for parents to vaccinate their offspring, the Speaker of the House in Congress, John Boehner, said all children in the United States should be vaccinated. So far the outbreak, which has been traced back to the Disneyland theme park in California, has infected more than 100 people in the US.

Mr Christie, the Governor of New Jersey, made his comments on Monday while touring MedImmune, a medical vaccine company in Cambridge, during a three-day trade mission to Britain that ended today. He told reporters accompanying him that parents “need some measure of choice” on the matter.

In an interview with CNBC, Mr Paul was more forthright. “The state doesn’t own your children,” he said, adding that he had deliberately spread out the vaccinations of his own children so they didn’t receive too many at one time. He said he had “heard of many tragic cases of walking, talking normal children who wound up with profound mental disorders after vaccines”. But he offered no details.

A so-called “anti-vaxxers” movement has grown up in the US in recent years, thanks in part to a widely debunked 1998 report in The Lancet, the British medical journal, suggesting a link between MMR vaccinations against measles and the onset of autism in children.

On Sunday, President Barack Obama told NBC that every child should be protected by vaccinations. And on Monday, Hillary Clinton, widely expected to be the Democrat nominee in 2016, added her voice in a mocking Twitter post. Playing the granny card, she said. “The science is clear: The earth is round, the sky is blue, and #vaccineswork. Let’s protect all our kids. #GrandmothersKnowBest.”

Hillary Clinton offered her unequivocal support for vaccines in a Twitter post (Getty)

Mr Christie attempted to row back on his Cambridge remarks with a statement issued soon afterwards by his office in New Jersey. It said he believed “there is no question kids should be vaccinated when it comes to diseases like the measles”.

But by then his earlier remarks had already been seized on by the Democratic Party. “Chris Christie isn’t a scientist. He isn’t a doctor. And he sure as heck isn’t a leader,” Mo Elleithee, a spokesman for the party, said. “If his campaign is going to be about kissing up to the radical, conspiracy theory base that’s wagging the dog of today’s Republican Party, that’s up to him and his cracker-jack team.”

Among others leaping in to condemn both Republican White House aspirants was Seth Mnookin, a professor at the Massachusetts Institute of Technology, who challenged the “anti-vaxxer” camp in his book, The Panic Virus.

Their comments had been “incredibly, incredibly irresponsible,” he said, and “fail at the first duty of a politician, which is to calm his constituents in moments of irrational crisis”.

“All children should be vaccinated,” Mr Boehner said on Capitol Hill, while saying he wasn’t certain if there “ought to be another” law to enforce it. Presently, the issue is governed by state-level laws with many states allowing parents to opt out either on religious grounds or because of “personal beliefs”.

The sudden surge of measles cases has alarmed the Centre for Disease Control which in 2000 formally declared measles essentially eradicated from the US.