Media playback is unsupported on your device Media caption Public Health Wales said there had been an excellent response to drop-in vaccination clinics last weekend.

The number of cases in the Swansea measles epidemic has reached 620, with health officials warning there is no sign of the outbreak coming to an end.

The figure released on Tuesday is an increase of 32 on Friday, with up to 20 new cases being confirmed every day.

Public Health Wales said there had been an excellent response to drop-in vaccination clinics at a number of hospitals last weekend.

But it warned that 6,000 children in Swansea have still not had the jab.

Parents across Swansea, Neath Port Talbot and Bridgend are being urged to get their children vaccinated.

The total number of cases in the Swansea area is now 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.

Measles Q&A How safe is it to take children to mainland Europe who have had two doses of the MMR vaccine? It gives 99% protection against the measles virus. What if they have had only one dose of MMR? One dose is better than none, but two doses is better than one. If you are concerned about travelling to an outbreak area you can bring forward the second MMR dose. Speak to your GP about it. What if my children are not vaccinated at all? The advice is to go to your GP and arrange for them to be immunised as soon as possible before you travel. Measles is a dangerous viral illness that can be fatal. BBC Health - Measles 'Death risk' in outbreak

About 1,700 people were vaccinated at special hospital drop-in clinics at the weekend, which health officials called an "excellent" response.

But they say at least 6,000 children are still unvaccinated in the county of Swansea.

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.

'Not judging'

Dr Marion Lyons, director of health protection for Public Health Wales, said she believed the outbreak could go on for weeks.

"We cannot be confident that the outbreak will not continue to grow with so many children still at risk from this very contagious and potentially fatal disease," she said.

Some 60 people have been hospitalised since the start of the outbreak.

Sara Hayes, Abertawe Bro Morgannwg University Health Board's director of public health, said: "Many children who missed the MMR jabs when they were little will be sitting exams once they go back to school.

"We are not in any way judgmental about why their children may have missed the MMR in the past. The important thing is that they get the jab now," she added.

Analysis Around 6,000 children remain unvaccinated and with such a large deficit that means this highly virulent and contagious disease can still spread very quickly. On when it will peak, microbiologists will tell you it's almost impossible to know until the figures are in, but it's hoped the mass vaccination will start to have an impact within about a week or 10 days. If you look at the interval, we have had about 32 cases in four days, which is a slightly slower rate than last week. But we will get more figures later this week and it's probably too early to judge whether we are coming to the peak of this outbreak or not.

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.

A Swansea newspaper which joined the anti-MMR campaign at that time has defended itself against claims that it was to blame for the current outbreak.

Jonathan Roberts, editor of the South Wales Evening Post, said the campaign had been hard-hitting but reflected parents' concerns at the time about the safety of the vaccine.

"It is clear that there were genuine concerns in the mid-90s about MMR and the Post gave them full and responsible coverage," he said in Ean article for the paper.

"To judge it honestly and fairly, one has to consider the fear which existed at the time, the fact that medical experts were publicly expressing concerns about the vaccine and the duty of this paper to reflect public opinion."

Mr Roberts hosted a webchat on Tuesday on the paper's website.

He was asked to account for the fact that MMR vaccination rates dropped by about 2% across Wales but by 13% in Swansea.

Media playback is unsupported on your device Media caption Journalist Brian Deer tells how he discredited claims of a link between MMR and autism

"When looking back at the content contained within the stories we ran, the message was balanced," he said in response.

"We had a duty to reflect the concerns of our community, we also had a duty to reflect the official view of health professionals. And this we did."

He said he would be looking into republishing online archive stories from the time.

'Serious complications'

Although the epidemic is based in Swansea, cases continue to be reported across Wales.

Most are in the Abertawe Bro Morgannwg health region, which also includes Neath, Port Talbot and Bridgend.

There are also cases in Powys and in the Hywel Dda Health Board area, which covers Carmarthenshire, Ceredigion and Pembrokeshire.

Officials have said it is "just a matter of time" before a child is left with serious and permanent complications, such as eye disorders, deafness or brain damage, or even dies.

Typical symptoms of measles include fever, cough, conjunctivitis and a rash. Complications are quite common even in healthy people, and about 20% of reported measles cases experience one or more complication.

These can include ear infections, vomiting and diarrhoea, pneumonia, meningitis and serious eye disorders.