There are growing fears over the safety of children in Swansea after the number of measles cases hit 620, with the epidemic showing no signs of slowing.
More than 1,700 MMR jabs were dished out at emergency centres over the weekend, and still Public Health Wales (PHW) has warned that there is no sign of the outbreak coming to an end.
As many as 6,000 children remain unvaccinated in the county alone, it said, fuelling fears over a potential death from the illness.
"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,” said Marion Lyons, Director of Health Protection for PHW.
Those not vaccinated are highly likely to contract measles, "and 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 dies," the agency stressed.
Given the seriousness of the situation, a US-based measles expert has urged ministers to consider mandatory vaccinations with the MMR jab, as happens across the pond.
Paul Offit reportedly told BBC Newsnight: "In this country we just don't think its your inalienable right to catch and transmit a potentially fatal infection and so we at least put that one hoop you have to jump through which is mandatory vaccination."
But the Welsh government has seemingly rejected this suggestion; a spokesperson told the BBC that it felt "the hard-won trust in the MMR vaccine and in GPs would be damaged by introducing compulsory vaccination".
The outbreak comes despite leap in uptake of the MMR vaccine from 2002, when coverage was less than 80%, with 93% of eligible children in England now getting the first dose and 87% the second dose, and 95% and 88%, respectively, in Wales.
Uptake of the jab took a huge downturn after 1998, when Andrew Wakefield sparked a major health scare with his paper - published in the Lancet - linking the MMR vaccine to a syndrome characterised by autism and bowel disease.
Twelve years later the journal retracted the study after an investigation by the General Medical Council revealed several elements of the paper were incorrect, and in 2011 a report by the British Medical Journal concluded that it was actually based on falsified data.
Still the damage was done, and many parents avoided the jab on fears it could harm their children.