CAMBRIDGE, England - After Gov. Christie said Monday that parents need "some measure of choice" on vaccinating their children, stirring alarm that such views would hurt the fight against a measles outbreak, his office moved quickly to clarify his position.

The dustup overshadowed the second day of what Christie has planned mainly as a trade mission.

Monday morning, the Republican governor, a potential candidate for president in 2016, responded to a question about the spread of measles by saying that while he and his wife had their children vaccinated, parental concerns warrant "balance."

"It's much more important, I think, what you think as a parent than what you think as a public official," Christie told reporters. Christie had just toured one of the biotechnology company MedImmune's laboratories. The company makes a flu vaccine.

In January, more than 100 cases of measles in 14 states were reported, the majority involving patients who were unvaccinated, according to the federal Centers for Disease Control and Prevention.

While some parents believe the vaccine will lead to increased risk of autism, medical experts - including the American Academy of Pediatrics - say studies have not borne out such a link.

New Jersey Assemblyman Herb Conaway (D., Burlington), a physician and chairman of the Health and Senior Services Committee, said in a statement that the governor's "wavering comments are irresponsible and endanger the health of our communities." He called on Christie to "unambiguously" support vaccinations.

"Choosing not to vaccinate your child could also endanger the health of other children in your community," Tom Frieden, the CDC's director, said at a briefing.

Christie was backed by a fellow Republican White House prospect, Kentucky Sen. Rand Paul. Paul said in a radio interview that while vaccines were "a good thing," they should be voluntary.

"I have heard of many tragic cases of walking, talking, normal children who wound up with profound mental disorders after vaccines," Paul, an ophthalmologist, said later. "But I think the parents should have some input. The state doesn't own your children."

Paul's staff, too, sent out a statement later saying that the senator "believes that vaccines have saved lives" and that "his children were all vaccinated."

Christie said vaccinating his own children was "an important part of making sure we protect their health and the public health."

The governor - criticized last year by public health experts for announcing a mandatory Ebola quarantine policy - added, however, that parents "need to have some measure of choice in things as well, so that's the balance that the government has to decide."

The balance "depends on what the vaccine is, what the disease type is, and all the rest," Christie said, without naming any vaccines or diseases.

His remarks spread on social media, and by midafternoon - after Christie had laid wreaths at a memorial in a cemetery for American World War II veterans and stopped at a pub for lunch - his office had issued a new statement.

"The governor believes vaccines are an important public health protection and with a disease like measles there is no question kids should be vaccinated," said the statement, sent by spokesman Kevin Roberts.

"At the same time different states require different degrees of vaccination, which is why he was calling for balance in which ones government should mandate."

Christie did not address a pack of reporters who waited outside 10 Downing Street Monday evening while he met with Prime Minister David Cameron, emerging after 45 minutes in the prime minister's residence and walking straight to a nearby van. He was scheduled to dine with cabinet ministers.

Earlier in the day, Christie took part in a closed-door meeting with pharmaceutical executives and investors that focused in part on an expanded research program at Rutgers University, the governor said.

He then put on a lab coat and goggles for a tour of MedImmune with his wife, Mary Pat, getting a lesson in antibody drugs.

At one point the governor quipped, "Now I know just enough to be dangerous."

The measles outbreak, traced to Disneyland in Southern California, has raised questions about vaccinations. On Sunday, President Obama said in an NBC interview that there was "every reason to get vaccinated, but there aren't reasons to not."

"I understand that there are families that, in some cases, are concerned about the effect of vaccinations," Obama said. "The science is, you know, pretty indisputable."

When he ran for governor against Democratic incumbent Jon S. Corzine in 2009, Christie said he supported families affected by autism who were worried by "New Jersey's highest-in-the-nation vaccine mandates," according to a letter from his campaign.

"I stand with them now, and will stand with them as their governor in their fight for greater parental involvement in vaccination decisions that affect their children," the letter says.

The letter was posted on a vaccination-choice website run by Louise Kuo Habakus, who wrote a book called Vaccine Epidemic.

Habakus, of Middletown, N.J., said that she received the letter in 2009 and that Christie's response Monday was in line with what he had said previously.

"He's saying, 'I want to hear from parents. I want to hear what their concerns are. I want to know why they're worried,' " Habakus said.

Christie is "not saying, don't vaccinate. He's not saying vaccines cause autism," Habakus said. "But he's not saying they don't, either."

Roberts said Christie "met with a lot of families of autistic children in 2009 who were concerned with New Jersey's high autism rate. He listened to what these families had to say, just as he would with a lot of different communities."

Christie's trip is being paid for in part by Choose New Jersey, a nonprofit organization funded by businesses that recently hired departing state Economic Development Authority chief Michele Brown as its chief executive.

The group, which also sponsored trade missions Christie led to Mexico in September and Canada in December, has not disclosed the costs of the two trips.

The state has said it is covering Christie's security costs for the trips, but also has not disclosed the costs.

"What businesses get out of it, we hope, is a more vibrant, and effective and growing New Jersey economy," Christie said Monday. "And that's good for every business."

Of Choose New Jersey's sponsorship, Christie said, "That's their choice, and these businesses have the freedom to invest what they want to invest in."