Four emergency clinics have given around 1,200 people measles vaccinations across south Wales.
Health officials said demand for the vaccine was 50 per cent higher than anticipated, as hundreds queued at the four hospitals offering free MMR jabs.
They were at Morriston, Singleton, Neath Port Talbot and the Princess of Wales hospitals.
So far almost 600 people have been affected by the measles outbreak, focused around Swansea. The emergency clinics arranged for today aim to stop the virus spreading to neighbouring areas.
The number of confirmed cases of measles in the epidemic had risen to 588, with over 40 new cases since Wednesday.
Health officials have estimated around 3,800 children in the Swansea area have still not had the MMR vaccine and parents are being asked to act.
And today the number of confirmed cases of measles across England's north-east reached 200.
The Health Protection Agency has already declared the outbreak as one of the worst in recent years.
Since September there have been 200 confirmed and 176 suspected cases, compared to just 18 confirmed in 2011.
Dr Marion Lyons, Director of Health Protection for Public Health Wales, said: "The alarming numbers of cases of measles and continuing spread of the disease in Wales illustrates how vital it is for parents to get their children vaccinated.
"Unvaccinated children aged between six and 12 months living in or travelling to the outbreak areas of Swansea and Neath Port Talbot can be offered vaccination by their GP.
"There's no adverse effect to this extra jab and those children would still need to receive the recommended two doses at 13 months and three years four months."
Dr Lyons added that increasing numbers of people coming forward for the MMR vaccination was encouraging - with just under 600 people in the Abertawe Bro Morgannwg University Health Board area alone receiving an unscheduled MMR vaccine in the past seven days.