Ten cases of mumps have been reported in Northland this winter as an outbreak of the illness sweeps communities in Auckland and further afield.
There have been 440 cases recorded in New Zealand since January, which is more than all the cases over the previous 16 years, after a serious outbreak of up to 300 cases in 1994.
The total Northland cases since that outbreak has been 69.
"There were no reported cases at all in 2016 and only three in 2015, so this is quite a change for us," said Dr Simon Baker, Northland District Health Board (NDHB) Medical Officer of Health.
There is no real pattern of contagion in the Northland cases.
Some have been confined to one family, and some have been individual cases in various communities.
As in Auckland, mostly children and young people have been hit with the mumps in Northland.
While mumps is a notifiable disease not all cases look typical, so some people will have had it without knowing, Dr Baker.
"Other people will have suspected they had mumps, but not gone to the doctor. So, there will almost certainly be other cases in the community that we do not know about, but that happens with most notifiable diseases," Dr Baker said.
The disease poses a risk to young people who have not been vaccinated with two doses of the MMR vaccine, he said.
Mumps is an infectious viral illness which can cause fever, soreness, swelling in the face and general malaise.
Most people recover after a few weeks, but mumps can have serious complications.
The disease can cause inflammation of tissue surrounding the brain (meningitis), inflamed testicles or ovaries, permanent deafness and infertility.
A large number of 10 to 29-year-olds - dubbed the "lost generation" by health officials - are at risk of mumps, measles and rubella after some parents rejected the MMR (measles, mumps and rubella) vaccine which was at the centre of controversy in the 1990s.
Meanwhile winter viruses are on the retreat, judging by the number of serious cases presenting at Northland hospitals.
Nationally, since last week there has been a drop in the influenza seasonal threshold according to data from ESR (Institute of Environmental Science and Research). The influenza strain this year was A H3N2.
Respiratory syncytial virus (RSV) is the other respiratory virus that kept GPs and hospitals busy this winter, with many young children presenting with bronchiolitis.
"The tail end of the winter viruses should taper off with the October school holidays, which anecdotally do seem to help reduce transmission," the NDHB said.