At least 5,000 children in an area hit by a measles epidemic have yet to have the MMR jab despite a massive vaccination take-up over Easter.
Numbers of children with measles in the Swansea area will continue to rise over coming weeks before the spread of the disease peaks, experts warn.
The South Wales epidemic is one of the largest measles outbreaks to hit Britain in the last decade.
The number of sufferers stood at 693 at the end of last week after 73 cases were reported in two days.
Health Secretary Jeremy Hunt has urged parents who chose not to get their children vaccinated to act now.
Andrew Wakefield was struck off the medical register for his discredited research which claimed to find a link between autism and the MMR vaccine.
The study, published in 1998, caused a global scare and, in the following years, uptake levels of the vaccination - which protects against measles, mumps and rubella - fell significantly
Today Mr Hunt said: “Disgraced doctor Andrew Wakefield's discredited and inaccurate research caused great harm to the MMR vaccination programme and led to thousands of parents choosing not to vaccinate their children against measles, mumps and rubella.
“Today I am urging all parents, anywhere in England, who did not get their child vaccinated with two doses of MMR because of scare stories a decade ago to contact their GP surgery and make an appointment.”
Special vaccination sessions at four hospitals in South Wales saw thousands flock to get their children vaccinated over Easter.
A total of 1,750 MMR jabs were given during the first weekend of the school Easter break and a further 1,700 at similar sessions on Saturday.
Vaccination sessions are due to begin tomorrow at a handful of schools in the worst-affected areas.
But while progress has been welcomed by Public Health Wales it is estimated that up to 40,000 children across Wales remain unprotected.
And Mark Drakeford, Wales' minister for health and social services, warned today that the numbers affected will continue to rise.
"It is important for us all to remember measles is not a trivial illness. In a minority of cases, it can lead to serious complications and it can be fatal," he said in a written statement.
"Regrettably, the more the disease continues to spread, the more likely these outcomes become. It is vital we build on the progress made so far and bring the outbreak under control."