There are 15,000 children in Northern Ireland who have not been fully vaccinated against measles, mumps and rubella in the last seven years, a new Audit Office report has said.
The report from Comptroller and Auditor General Dorinnia Carville into pre-school vaccinations highlighted particularly low levels of vaccination uptake in the Belfast area.
Ms Carville said while there was no single reason for declining rates of vaccination, delivery capacity within GP practices in Northern Ireland is likely to have contributed.
The report considered outcomes of vaccination against 14 infectious diseases among pre-school children. It found that for 13 of the diseases, vaccination rates in Northern Ireland have been steadily declining.
The World Health Organisation (WHO) vaccination target is 95% to ensure population immunity.
The report found overall vaccination coverage has steadily been declining for almost all diseases and increasing numbers of children have not received all the vaccinations available to maximise protection against harmful diseases.
Across Northern Ireland, there are 15,000 children who have not been fully immunised against measles, mumps and rubella (MMR) over the last seven years.
The report also said that a total of 10,200 children have not received all the recommended doses of the Pneumococcal Conjugate Vaccine (PCV) since 2015.
It said that while this downward trend in coverage is reflected in other parts of the UK, data reveals regional variation in the uptake of vaccinations, with particularly low levels in Belfast.
Within the Belfast Health and Social Care Trust area, one in three children has not been fully immunised against pneumococcal disease since 2015, and one in seven has missed "six-in-one" vaccine doses which protect against multiple diseases over the last seven years.
The report said that vaccination rates in three of Northern Ireland's five health trusts were close to or above the WHO target.
Ms Carville said: "Vaccination against infectious disease remains one of the most successful and cost-effective ways to help manage the health of a population.
"However, as many vaccine-preventable diseases require a series of immunisations to be administered to infants and small children at pre-determined intervals, overall effectiveness is heavily reliant on consistently high levels of participation.
"Whilst there is no single reason for the declining rates of vaccination coverage shown, workforce shortages and delivery capacity within GP practices in Northern Ireland are likely to have contributed to the overall trend.
"It is hugely important that there is a comprehensive plan of action to reverse the decline."
The report said the success of any large-scale vaccination programme will be dependent on addressing issues including "the lack of clarity in roles and responsibilities which has arisen in relation to the administration of vaccinations provided through GP practices" and "the fact that some GPs have not met vaccination coverage targets set by the Department of Health".
The report also looked at the seasonal flu vaccine which has been administered to children between two and four years of age since 2013-14.
It said that for the 2019-20 season, a vaccination target of 60% was set by the Department of Health (DoH) for this group. However, the coverage achieved was 48.5%.
The report said that even with an improved uptake (55.2%) for the 2020-21 flu season, rates of coverage continued to be well below target.
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