This article was written by James Meikle, for guardian.co.uk on Tuesday 16th April 2013 12.27 UTC

The number of measles cases reported in the Swansea outbreak has risen by more than 10% in a week to 765, according to Public Health Wales.

The total rose by 72, and 77 people have now been taken to hospital during the crisis. Health officials and ministers have warned that more people will catch the highly infectious disease as they attempt to bring the outbreak under control.

They are stepping up pressure on parents across Wales to ensure their children are vaccinated with the triple measles, mumps and rubella (MMR) vaccine.

Public Health Wales said it was "just a matter of time" before a child died or was left with serious or permanent complications such as eye disorders, deafness or brain damage. Five thousand children in the Swansea area alone are said to remain at risk and children between 10 and 18 have been most affected so far.

Meanwhile, a measles outbreak in north-east England is also getting worse with a more than 10% rise in suspected cases over a week. In all, 214 cases have been laboratory confirmed and another 220 suspected since numbers began to rise last September. Nearly a third of all cases have involved children aged 10 to 14 and nearly one in six of all those affected have need hospital treatment.

On the Welsh outbreak, 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.

"We can’t bring this outbreak to an end unless the parents of unvaccinated children either arrange vaccination with their GP, call in to one of the weekend drop-in sessions or ensures that if their child attends a school where vaccinations are being offered, they have signed a consent form for them to be vaccinated.

"Children who do not have signed consent forms cannot be vaccinated so it is crucial that parents ensure they have given their consent."

The highest attack rate was in children aged 10 to 18. "These are the children who may not have been vaccinated because of concerns about the safety of MMR in the late 1990s. The vaccine is safe, effective and the only protection against a potentially fatal disease," said Lyons.

"Although the outbreak is at present affecting the Abertawe Bro Morgannwg, Powys and Hywel Dda health board areas, we have cases of measles in every health board area in Wales and we have no way of knowing where the outbreak might spread. As children return to school after the Easter holidays, the opportunities for measles to spread increase. Now is the time to vaccinate your children."

Although nearly 3,700 children were given catch-up jabs at special clinics over the past two weekends, and hundreds more pupils will be immunised at schools and GP surgeries in Swansea and across Wales, Mark Drakeford, the health minister, said: "It is vital we build on the progress made so far and bring the outbreak under control."

Drakeford said in a written statement to the Welsh assembly in Cardiff: "It is encouraging parents are continuing to bring their children forward but the numbers need to be higher to bring the outbreak under control."

He anticipated the numbers of cases would continue to rise over the coming weeks until vaccination uptake reached levels where "the continuing circulation of measles in the community can be interrupted".

Drakeford said: "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. Regrettably, the more the disease continues to spread, the more likely these outcomes become."

He said figures for Wales from the end of last year showed that uptake of the MMR vaccine for the first of two jabs was now 94.3% of two-year-olds, whereas uptake of the second dose at five had reached 89.9%.

"While more infants are having the vaccine now, efforts must be focused on those children who missed out for whatever reason in the past so that they are offered catch-up vaccinations to provide maximum protection to the community as a whole."

Officials in Wales are only releasing reported numbers as they try to get the vaccination message across.

All new cases reported in the outbreak in north-east England come from the Teesside area, but public health doctors there say the risk of measles across the region remains high. Last month they asked all schools on Teesside to send letters to parents alerting them to the increase in measles cases and asking them to check their children had been immunised.

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