A nationwide outbreak of mumps has caused more than 1,600 infections this year and may flare up again as schools and colleges return next month, the HSE has warned.

The biggest mumps outbreak in a decade continues, and the number of cases is still above normal levels. However, the weekly number of cases is declining, according to the HSE’s Health Protection Surveillance Centre.

The worst-affected area is Dublin and neighbouring counties and the largest number of cases has occurred in 15- to 24-year-olds.

Doctors say the MMR vaccine is the best way to prevent the disease and its complications, though it is estimated to be only 88 per cent effective in preventing mumps.

“When schools and universities recommence in September, there is a potential for increased numbers again as the close social contact in these settings can contribute to spread,” the HPSC has warned.

It says a “substantial minority” of cases in the 15-24 age group reported having received one or more doses of MMR. “The vaccine effectiveness is approximately 88 per cent and there is increasing evidence that the effectiveness may wane over time. Despite this, the vaccine continues to be the best and only way to prevent, or minimise the risk of infection and complications associated with mumps.”

Mumps is an acute viral infection spread from person to person. Symptoms include fever, headache, tiredness and swollen and tender salivary glands. Mumps often gives the appearance of swollen cheeks or jaw.