The preliminary findings of an investigation into the outbreak said the introduction of the MMR vaccine in Ireland in 1988 combined with improvements in measles control had contributed to a lack of familiarity with measles among doctors.
“In this outbreak, diagnostic delay occurred for some of the early cases due to lack of recognition,” the report stated.
Researchers led by HSE officials said it had also led to a delay in isolating cases and further transmission of the disease in hospital settings.
A total of 22 confirmed cases and five probable cases of measles were reported between April 1 and June 13. More than two-thirds of all the cases were detected in Kerry. Some cases were also reported in Dublin, the mid-west and north-east.
Seven cases involved children under the age of 4 years, In contrast, only one incidence of measles had been notified to the authorities in the first three months of the year.
The source of the latest outbreak was traced to a child who had travelled from Romania to Ireland via Hungary in mid-April.
The child had been unwell with a fever and rash on the flight to Dublin.
The child travelled to the south-west on arrival and was then hospitalised, although she was not tested for measles on admission, nor was she immediately isolated.
Given the incubation period, doctors said it was most likely that exposure to measles occurred in Romania.
Almost half of all cases involved members of the Roma community, all of whom were unvaccinated.
Five cases became infected through contact in a hospital or doctor’s surgery, while three patients were infected on a flight.
Researchers said the latest outbreak highlighted a number of challenges and learning points for the public health authorities in Ireland.
MMR vaccinations rates among children have increased slowly over the past 15 years moving from fewer than 80% in 2001 to around 93% currently.
However, it is still short of the official target vaccination rate of having 95% of all children given one dose of MMR vaccine by 24 months of age.
The incidence of the disease has declined from 8.4 cases per 100,000 in 2004 to 0.7 cases per 100,000 in 2014.
The report said immunity gaps persisted among both newborn babies and older children.
It also noted that most cases in the latest outbreak involved children who were unvaccinated. Twenty-four of the 27 cases had not received the MMR previously.
Researchers said the number of notified cases of measles was likely to underestimate the true number of cases.
The report said the cost of the investigation of the latest measles outbreak was “likely to be considerable” as 45 staff were involved in managing the outbreak nationally.
“The cost of vaccination for measles prevention may be relatively small when compared with outbreak control efforts,” it observed.
However, it acknowledged that the outbreak had shown the benefits of rapid information exchange between multiple agencies as well as between EU member states, which enabled public healthcare staff to trace the likely source of infection.