Around 72 cases of measles have been reported to Public Health Wales since Thursday and a total of 77 people have been hospitalised since the outbreak, the largest in the UK for over a decade, began.
Around 50 cases of measles were reported at the beginning of the year in Wales. This more than doubled to 288 in March. So far 257 cases have been reported this month.
The measles virus is expected to spread further now that children have returned to school after the Easter holidays.
It is estimated that around 5,000 children still remain at risk from measles in the Swansea area alone.
Parents are being urged by Public Health Wales to work with health professionals and schools to ensure their children are vaccinated against measles with the combined Measles, Mumps and Rubella vaccination, known as MMR.
Vaccinations are being offered to parents in the Swansea area, which has the highest reported number of cases, to try to end the outbreak and ensure children of all ages are protected against the three viral illnesses.
Efforts are now being focused on older children who missed out on having the vaccination in the past in order to provide maximum protection to the community.
Four Swansea schools and one in Neath are holding drop-in-clinics to give unvaccinated children the MMR from today.
Drop-in-clinics have also been held in the area on the last two Saturdays, which Public Health Wales says have had an excellent response.
The MMR is offered to children between 12-13 months of age. They receive the second dose before they start school, usually between three and five years of age.
According to Public Health Wales’ figures for October to December 2012, 89 per cent of children received the second MMR dose by the age of five.
Experts believe to successfully eliminate measles, 95 per cent of a country’s population needs to be immunised with two doses of the measles vaccine.
While there is no guarantee that children vaccinated in the last two weeks will not contract measles, the virus is likely to be milder than if they had not received the vaccine, says Public Health Wales.
Dr Marion Lyons, director of health protection for Public Health Wales, said, ‘Plenty of opportunities are being offered to parents to vaccinate their children against measles, but parents need to make sure they take these opportunities.
‘Measles cannot be taken lightly because you can never tell who will go on to develop the more serious complications of pneumonia or encephalitis - inflammation of the brain. MMR vaccination offers the only protection against these complications.’
The MMR vaccine is given in two doses. The first is offered to children when they are between 12-13 months of age. They are given the second dose before they start school, usually between three and five years of age.