A slight change in the mumps virus and previous false claims about a link with autism are two of the reasons why the virus is spreading at present.
The increase in incidences has been particularly noticeable in secondary and third-level educational institutions.
As a result, the HSE is urging anyone aged between 11 and 30 who has not had two doses of the MMR vaccine to avail of the offer of a free dose.
Dr. Anthony Breslin, specialist in Public Health Medicine in the north west, has been telling Ocean FM why there’s now an increase in cases.