Health chiefs in Wales have warned that youngsters who have never had the MMR jab could potentially be left brain-damaged or dead by a growing measles outbreak.
During the last week there have been 64 extra cases diagnosed in Swansea, south Wales, taking the overall number of those affected to 316.
This latest seven-day report shows an increase on the week before when there were 43 extra cases reported, taking the infection rate at the time to 252.
Public Health Wales (PHW) confirmed that 42 people have been admitted to hospital after contracting the disease, which has spread to youngsters across 111 secondary and primary schools, playgroups and nurseries in the area.
So far most cases have been reported in and around Swansea, but health officials confirmed that there are increasing reports of cases in the Mid and West Wales areas.
With that in mind, parents of all children aged between one and 18 in Wales who have not been vaccinated have been told to contact their GP immediately for advice and to arrange vaccination.
Dr Marion Lyons, PHW director of health protection, said that it cannot be stressed enough that measles can be a fatal illness.
She explained that measles is so infectious that 90% of unvaccinated people who come into contact with the disease end up catching it themselves.
Dr Lyons added that all it takes is for a few people who haven't had the jab to put at-risk individuals, such as children with leukaemia who cannot have it, in danger.
"We cannot emphasise enough that measles is an illness that can kill, or leave people with permanent complications including severe brain damage. The only protection is the safe and highly effective MMR vaccine," she added.
Copyright Press Association 2013