Mumps jab can fail with time

With the country in the grip of its worst mumps outbreak in decades, an infectious diseases doctor is warning people vaccinated against the disease as children can lose their protection over time.

Instances of swollen testes caused by mumps are being reported, a condition that can lead to infertility in men.

Dr Ayesha Verrall, a researcher at Otago University in Wellington, is calling on the Ministry of Health to ‘‘urgently’’ fund a third dose of the vaccine for people aged 10 to 29 who had already received the recommended two doses of the measles, mumps and rubella (MMR) vaccine.

Catch up vaccinations for people who aren’t already fully vaccinated are free.

Interventions announced so far by the Ministry of Health targeted vaccination at people who were never vaccinated or those whose vaccinations weren’t ‘‘up to date’’. It would miss people whose vaccine protection had waned, Verrall said.

‘‘Failing to address this fact limits our ability to respond to control the outbreak meaning mumps will disrupt education, sports and community activities for young people for the next several years.’’

‘‘Failing to communicate that previously vaccinated people are susceptible also risks undermining public confidence in vaccines.’’

While the vaccine was about 90 per cent effective, its protection reduced over time. ‘‘While most people vaccinated in childhood will still be protected, many will learn they were in fact susceptible to mumps when they catch the disease,’’ Verrall said.

Recent studies had shown that during an outbreak, young adults in high risk settings could benefit from a third dose of the MMR vaccine, even if they completed their two doses as a child.

The mumps outbreak started in Auckland in early 2017. More than 1000 cases have since been reported, some from centres other than Auckland.

Because vaccinated people could lose their protection from mumps over time, a significant minority of the people who had developed mumps in the outbreak were vaccinated, Verrall said.

Added to the problem that protection from the vaccine reduced over time, uptake of the MMR vaccine had been low when people who were now adolescents and young adults had been children.

Verrall is critical of efforts made to contain the disease. If health authorities had been serious about stopping the outbreak, a catch up vaccination campaign for adolescents and young adults who were not fully vaccinated should have started five years ago, she said.

Mumps causes a fever, headache, muscle aches and most cases have swollen salivary glands, usually on both sides of the face. It is spread from people by saliva or mucous droplets spread when coughing. Occasionally it can cause serious complications like meningitis and hearing loss. Because it is caused by a virus, antibiotics are not effective treatment.