As a measles epidemic in south Wales continues to spread at an "alarming rate" an expert has said mandatory vaccinations should be considered.
Dr Paul Offit, a US-based measles expert, told the BBC that mandatory vaccinations in America had prevented similar outbreaks.
His comments came as measles cases in the Swansea area rose to 620.
The Welsh government said it believed the "hard won trust" in MMR would be damaged if vaccination was compulsory.
Public Health Wales (PHW) said there were no signs of a slow down in cases.
Speaking on BBC Newsnight, Dr Offit said Britain would benefit from American-style mandatory vaccinations.
People in the United States can still claim exemption on philosophical or religious grounds but Dr Paul Offit said it still increased vaccination rates.
"If we didn't mandate vaccines I think we would suffer in many ways what's going on in Europe now," Dr Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia, said.
"Many children are needlessly suffering this disease and being hospitalised by this disease and occasionally being killed which I think is unconscionable.
"In this country we just don't think its your inalienable right to catch and transmit a potentially fatal infection and so we at least put that one hoop you have to jump through which is mandatory vaccination."
The Welsh government said it was not considering compulsory vaccination at present and that they were seeing a "much improved uptake in vaccination rates now".
A spokesman said: "The current epidemic, affecting school age children in particular, is the legacy of a damaging and unfounded health scare in the late 1990s.
"Since then, trust in the MMR has been regained, to the point where almost 95% of pre-school children are vaccinated. We believe that at this point, the hard-won trust in the MMR vaccine and in GPs would be damaged by introducing compulsory vaccination."
Health officials dealing with the outbreak in the Swansea area said despite 1,700 people being vaccinated with the MMR jab at drop-in clinics at the weekend, the spread of the disease was still rising.
Experts said they were not seeing enough children aged 10 to 17 coming forward for the jab.
PHW estimate 6,000 children have still not been vaccinated, with the outbreak still not peaking.
Parents across Swansea, Neath Port Talbot and Bridgend are being urged to get their children vaccinated with GPs.
Dr Marion Lyons, director of health protection for PHW, warned there was no sign of the outbreak, which began last November, easing.
"We're getting a lot of new cases in this week," Dr Lyons told BBC Radio Wales.
"And because so many are unvaccinated still, you know they will infect so many more that we will see next week and the week after because of the long incubation period.
"It is still rising at an alarming rate."
More hospital drop-in clinics will be held in Swansea, Neath Port Talbot and Bridgend on Saturday, targeting children and adolescents who did not have their scheduled MMR (measles, mumps and rubella) jabs as babies and toddlers.
Some GP surgeries are also laying on special vaccination sessions, while children will be given the jab at schools in the outbreak area when they return next week after the Easter break.
Dr Lyons said it is the older children who are now most at risk from the disease because parents have taken babies and toddlers for vaccination in recent days.
"Most of our cases are occurring in the 10 to 17 year olds. That's the population where a lot of them haven't had the vaccine," she said.
"They'll go back to school next week, they'll be playing together, socialising together and they will spread it."
She said the public health trust has written to every parent about vaccination.
Concerns over the safety of the MMR jab were raised in the late 1990s when a surgeon published a since discredited paper in The Lancet suggesting MMR was linked to an increased risk of autism.
That paper, and subsequent media coverage, led to immunisation rates plummeting.
But Dr Lyons also said she did not believe parents were concerned any longer about the "myth" surrounding the MMR jab.
"I don't think that is the issue now," she said.
She said parents of normally healthy older children, who don't visit GPs and miss spot-checks, can forget they are at risk of measles.
"I think it is a case of just reminding the parents that their children are just as vulnerable as the little ones," she said.
Health Minister Mark Drakeford thanked NHS staff for their response to the measles outbreak and said it was "vital to maintain momentum" of people having vaccinations.
"Those not vaccinated are highly likely to catch the disease as measles is still circulating, and we still face the awful possibility of a child left with serious and permanent complications such as eye disorders, deafness or brain damage, or dying," he added.
The total number of measles cases in the Swansea area now stands just two short of the total in the outbreak in the north west of England in the year to February 2013.
Most of these cases were on Merseyside, in Greater Manchester and west Lancashire.