Worn-out mumps vaccine can leave people at riskby Ruth Nichol
Today the All Blacks, tomorrow the rest of us, as worn-out mumps jabs leave people vulnerable.
“It’s pretty good, but it’s not up there with measles and rubella, which are quite remarkably effective,” she says. “We see the mumps vaccine start to wane after 10 to 15 years. That means we’re going to see more mumps outbreaks in highly vaccinated populations, especially people who are getting up close and personal, which infectious diseases adore.”
Vulnerable groups include sports teams – “the All Blacks are a perfect example” – or, as happened in the US recently, university halls of residence. The good news is people who have had two doses of the MMR vaccine at ages one and four have fewer serious complications if they do get mumps in their twenties. Possible complications include meningitis and permanent deafness, as well as inflammation of the testicles in men and of the ovaries in women, both of which may affect fertility.
The All Blacks cases come at a time when New Zealand is experiencing its biggest mumps outbreak since 1994. More than 900 cases have been reported so far this year, most of them in Auckland. And although a few people may have caught the disease despite being fully vaccinated, Petousis-Harris says most cases have been in people who are unvaccinated.
She says the outbreak, which is believed to have been sparked by cases from Fiji and Tonga, where the mumps vaccine is not available, is the result of a perfect storm of contributing factors. These include historically low vaccination rates, which mean that a cohort of 12- to 29-year-olds never had the MMR vaccine after it was introduced in 1990 and are not protected against mumps. Older people already have immunity because they had the disease as children.
Another group of twentysomethings may be susceptible to infection because they missed the second dose of MMR when its timing changed from 11 years to four years in 2001. The second dose is particularly important to increase the effectiveness of the mumps part of the vaccine. “It’s not a booster – it’s given because not everyone responds to the first dose.”
Others may have caught mumps because they come from countries that don’t vaccinate against it.
“Every year, we got more non-immune people in the population, then finally we reached a critical threshold and whoosh – we’ve got a major outbreak.”
Public health authorities have leapt into action, with the Waitemata District Health Board now running a school-based campaign targeted at unvaccinated teenagers. Petousis-Harris says others in the at-risk age group can get free catch-up vaccinations through their GP. “If you have no evidence that you’ve had two doses of the MMR vaccine, book yourself in and get them. There’s no harm in having an extra dose.”
Mumps is a relative newcomer to the childhood immunisation schedule. A measles vaccine was first introduced in New Zealand in 1969, followed by one for rubella in 1970. But we didn’t start vaccinating against mumps until the MMR vaccine was introduced in 1990.
At that time, New Zealand vaccination rates were shockingly low. A study in the early 1990s found that fewer than 60% of two-year-olds were fully immunised, and the numbers were even lower for Māori and Pasifika children.
These days, thanks to a concerted effort by health officials and the introduction of a national immunisation register in 2004, 89% of five-year-olds are now fully vaccinated.
“The register means we can measure the overall coverage, which was very difficult to do before. We can also see who has and who hasn’t been immunised and we can call them and recall them.”
For those of us who grew up when everyone got mumps, it may seem a harmless illness. Petousis-Harris says it is less serious than measles and rubella. But it can still cause worrying complications, such as permanent deafness.
“When everyone in a population gets mumps, you can end up with a lot of people with a disability. That’s what makes it worthwhile using a vaccine.”
This article was first published in the December 9, 2017 issue of the New Zealand Listener.
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