Almost one in 10 children in Portsmouth are not fully vaccinated against MMR, Public Health England South has revealed as the UK losses its measles-free status.
Across Portsmouth, 91.7 per cent of children were fully vaccinated against MMR, compared to 89.8 per cent across Hampshire, and just 85.2 per cent on the Isle of Wight.
Public Health England South East has warned that 14,000 5-year olds across the South East may not be fully up-to-date with their routine immunisations.
Clare Simpson, Immunisation Lead for Hampshire and Isle of Wight, said it was 'a real concern' that in some areas a quarter of children starting school this year have never competed their vaccinations.
She said: 'We know that parents want the best protection for their children and so many may be unaware that their child is not up-to-date.'
The figures have been released as the World Health Organisation announced the UK has lost its measles-free status, three years after the virus was eliminated in the country.
In the first quarter of 2019, there were 231 confirmed cases of the disease in the UK.
Only 87.2 per cent of children across the UK have had both of their MMR jabs, down from a high of 88.6 per cent in 2015.
Speaking during a hospital visit in Cornwall, Prime Minister Boris Johnson blamed 'superstitious mumbo-jumbo' on parents avoiding vaccinations, with the government to update advice on the NHS's website to address misleading information about the dangers of vaccines.
As part of the efforts to tackle the issue, NHS England will write to all GPs urging them to promote 'catch-up' vaccination programmes.
British Medical Association board of science chair Professor Dame Parveen Kumar said measures to improve vaccination rates were 'long overdue.'
She said: 'Doctors are very concerned that the number of young children who are up to date with vaccinations seems to be falling.
'Measles can be a very serious illness and whilst diphtheria and whooping cough are thankfully relatively rare, they remain a risk to children who are not vaccinated.'
Parents in doubt of their child's vaccine status are advised to contact their doctor.