The number of confirmed cases of measles in the Swansea epidemic has risen to 588, Public Health Wales has confirmed.
The latest figure shows 40 new cases of the disease since Wednesday.
Up to 20 new cases a day are being reported by GPs, with 109 new ones in a week over the Easter period.
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.
Special vaccination clinics have been arranged for this weekend, as fears grow about the virus spreading to neighbouring areas.
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.
"We are really pleased to see that 586 people have proactively got the MMR vaccine over the past week, on top of those already scheduled to have it," she added.
"Though this is a good start, there are still thousands of children who have not had both doses of the MMR jab and so are still at risk from becoming infected with the potentially fatal measles virus."
In the meantime, drop-in MMR vaccination clinics are being held by Abertawe Bro Morgannwg University Health Board between 10am and 4pm on Saturday April 6 at Morriston Hospital, Singleton Hospital, the Princess of Wales Hospital in Bridgend and the Paediatric Outpatients at Neath Port Talbot Hospital.
No appointments are necessary. Children and adolescents who have not had their scheduled MMR jabs will be targeted, but officials say "no-one will be turned away, including adults".