Fewer children were vaccinated against mumps and rubella last year, as only one childhood vaccine in Barnsley met the required target.
NHS figures show that 92.2% of teenagers in Barnsley have received two doses of the MMR vaccine by their fifth birthday in 2022-23, below the World Health Organization target of 95%.
The coverage rate also dropped from 93.5% the previous year.
Across England, 84.5% of five-year-olds have had their second dose of vaccine by 2022/23.
This is the lowest level since 2010/11.
Dr Gayatri Amirthalingam, consultant in medical epidemiology at UKHSA, said the downward trend was a “serious problem” that could be “life-changing” and even fatal.
She said: “The diseases these vaccines prevent, such as measles, polio and meningitis, can be life-changing or even fatal.
“No parent wants their child to get this disease, especially when it is easily preventable.
“Please do not delay and check now that your child has received all due vaccines.
“Check your child’s Red Book and contact your GP surgery if you are unsure.”
In the UK, babies also need to be vaccinated against meningitis B and rotavirus at eight weeks of age, as well as a “six-in-one” vaccine to help fight polio, tetanus, whooping cough, diphtheria, hepatitis B and influenza Haemophilus type b – A bacterium that can cause life-threatening infections.
Nationally, none of the vaccines met the World Health Organization’s 2022/23 targets.
In Barnsley, only one vaccine for infants and children met the 95% standard.
Dr Doug Brown, chief executive of the British Society for Immunology, said the UK was “still missing key targets”.
He added: “Vaccines are the safest and most effective way to protect our children from disease.
“Last year, uptake of 12 of the 14 childhood vaccinations fell, putting our communities at higher risk of infection and disease.
“Low vaccination levels mean harmful diseases can spread and infect unvaccinated people, including vulnerable groups who cannot be vaccinated, such as young children, people with compromised immune systems or people with cancer.”
A spokesman for the Department of Health and Social Care said it was vital that routine childhood vaccinations were up to date.
They added: “The UK has world-leading services and we have launched a number of catch-up campaigns to improve coverage, including a national catch-up campaign for MMR and London-specific campaigns for MMR and polio.
“We urge parents and carers to check that their child’s vaccinations are up to date and if not, they should make an appointment to catch up.”