Joining the dots: What’s really causing New Zealand’s measles epidemics

Hardline anti-vaxxers often cop the blame for New Zealand's frequent measles outbreaks - but researchers say an 'immunity gap' affecting an entire generation is what's allowing the disease to flourish.

Through a fog of sickness and sedatives, hooked up to oxygen in a hospital isolation unit, Cameron Edwards was just alert enough to realise something important: he was dying.

Days before, the lanky, fluffy-haired teenager had been tearing around with his brother at their Te Awamutu home in rural Waikato, scaring their mum Ally Edwards-Lasenby half to death with their antics. "He played rugby. He loved skateboarding. He loved BMX biking," she remembers. "He was a bit of a daredevil. I was always finding them jumping the bikes off something, or into some big puddle in the paddock."

Now, a measles infection had laid waste to her robust, healthy boy - and she knew what it meant to be really frightened for him. "I was watching my son deteriorate before my eyes and there was absolutely nothing that I or anybody else could do. It was up to his body to fight it."

A nurse had taken Edwards-Lasenby aside and explained the seriousness of the situation, and family members and some of Edwards' friends from intermediate began turning up at Waikato Hospital to see him. "I kind of clicked on when I started seeing everyone come in and be a bit extra-friendly," he says. "That's when it all got real."

Eight years later, he is 21 and very much alive - something his mum puts down to how strong he was before he got sick - but he remembers the fear that gripped him. "It sucks lying there dying. Seeing your family come in and say goodbye - it's shit."

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Edwards, who was never vaccinated against measles, was one of nearly 600 confirmed cases of the disease in New Zealand's 2011 epidemic. Now the country is in the middle of yet another significant measles outbreak - the fourth in a decade. Earlier this week ESR, the crown entity that tracks notifiable diseases in New Zealand, confirmed the number of cases so far this year had risen to 132, including 51 hospitalisations. The latest epidemic stretches from Northland to Canterbury and is made up of three distinct outbreaks, each traced to separate cases brought in from overseas.

The World Health Organisation (WHO) declared New Zealand free of endemic measles in 2017, which means it no longer circulates constantly in the population. Cases only occur when New Zealanders returning from overseas or international visitors arrive in the country carrying the disease. So why do those single cases keep turning into outbreaks? And what will it take to eliminate measles from New Zealand completely?

"Measles is like a heat-seeking missile," Nikki Turner, the director of the Immunisation Advisory Centre says. An airborne disease, it is incredibly infectious and WHO recommends that 95 percent of a population needs to be immune to stop single measles cases spreading further. New Zealand's current childhood vaccination programme prescribes two doses of measles-mumps-rubella vaccine (MMR): one at 15 months old and the second when children are four. Health authorities have managed to significantly increase national rates in the last decade, from 83 percent of two-year-olds in 2009 to 91 percent last year - not far off the WHO target. Some DHBs have met and even exceeded the target in some years, though lower rates persist in other areas - Northland, Bay of Plenty and West Coast DHBs all reported 85 percent or less last year.

But Edwards was born in 1997, right in the middle of a generation of New Zealand children who, for myriad reasons, have much lower immunity rates than the rest of the population. Now aged between 12 and 37 (with the lowest rates among 12 to 28-year-olds), they represent an "immunity gap" - and as long as that gap persists, New Zealand will never get rid of measles.

DHBs have worked hard to improve immunisation rates, Turner says. "However, the damage has been done historically. We have an awful lot of young adults and mid-life adults walking around, who are unaware whether they have or haven't had measles-containing vaccines. That is where our major problem is coming from."

Click here to see an interactive version of the chart above.

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The year after Edwards was born, leading medical journal The Lancet published a study linking the MMR vaccine to autism. The research has been thoroughly debunked in the years since, disowned by the The Lancet, and its lead author, Andrew Wakefield, struck off the UK medical register - but it went off like a bombshell at the time. The UK was the epicentre, but the shockwaves rippled through communities of parents around the world.

Edwards-Lasenby, an early childhood teacher, heard of the research while Edwards was still a toddler. She and Edwards' father had already chosen to delay their two boys' vaccinations, and the autism research seemed authoritative enough to decide not to go ahead with MMR. "It was conversations with other parents, it was on the news as well," she says. "And, being in my field, working with families with autistic children - I knew some of the challenges and watched the beautiful [but] hard work that they did as families."

Nikki Turner says the Wakefield study was one reason behind lower vaccination uptake between about 1991 and 2007. "[But] the main reason was our system did not deliver well to people, so people missed out."

The director of Massey University's Infectious Disease Research Centre, David Hayman, agrees with Turner. New Zealand's health system has funded a measles vaccine since 1969, but "immunisation programmes weren't wide-ranging enough and they weren't complete enough," he says. "Across New Zealand … there's still about 10 percent of the population that that we think are susceptible to measles … and we want that nearer to five percent."

In 2017, Hayman was the lead author of a measles study, funded and supported by the Ministry of Health, that resulted in articles in the international journals Vaccine and Epidemiology and Infection. As part of the study, researchers tested a sample population for measles antibodies to estimate just how low those immunity rates could be. "Even when we take the best estimate, some of these children that are now at high school, we've still got 16 percent of those that we think are susceptible to measles," Hayman says. And the worst estimate? "There were some cohorts where we got down to having 22 percent that we thought might be susceptible - those were people born between 1991 and 1995. And so that's really low."

Vaccination records for that period are as patchy as the uptake was. The National Immunisation Register - a centralised, digital database of which child has received what vaccine - was only introduced in 2005. Before that, those records were often only kept on paper: either GP records that were not necessarily transferred from practice to practice as families moved; or in Plunket and WellChild books, prone to getting lost in boxes of the usual jumbled-up family detritus - old bank statements, unsorted photographs, birthday cards and letters - in garages and attics across New Zealand. "If you've gone to the same GP all your life, fantastic, they'll be sitting there," Turner says. "But most of us haven't and so our immunisation records are all over the place."

The lacklustre outreach programmes and record-keeping over that period meant many families who made the decision many years ago to not vaccinate - or who just missed out through circumstance - were never followed up.

That included Ally Edwards-Lasenby, who says she made what she thought was the best decision for her children at the time, but was never offered the chance to revisit that. "Research is an ongoing continuum of information-gathering and it changes as new information becomes available. I had neglected to follow up that decision-making that I had done."

When Cameron Edwards and several other Te Awamutu children got measles in 2011, it prompted their local general practice to act, Edwards-Lasenby says. "They made a point of going through the records and identifying all those families around the same age as Cameron, that had chosen not to immunise and got in touch with them to give them updated information and offer immunisation… They had a number of families coming in and getting their children immunised."

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That is what both Nikki Turner and David Hayman would like to see happen, but writ large. The two researchers say a formal, publicised catch-up programme is the best way to close the immunity gap and ensure New Zealand stays measles-free. "New Zealand, I believe, needs to offer at least a single measles-containing vaccine to everybody under 50, who does not have a clear record," Turner says.

She concedes that without centralised records it would be a daunting task - but not impossible. "You can practically target it by geographical areas and age groups. We know that the higher rates [of non-immunity] are in people under 29.... We can go through general practice registers and recall people, remind them, recommend they come in. And we can do that systematically through the country, recognising that we would have to have [vaccine] stocks following as we do it."

The modelling Hayman and his team did concluded that about 100,000 unprotected people would need to be vaccinated to bring New Zealand's overall immunity close enough to the WHO target to stop most imported measles cases spreading beyond the original patient. "I think, yes, have a big catch-up scheme, and then the good work that's happening at the childhood immunisation levels will really be so beneficial."

On a more mercenary level, it would also save New Zealand money. The Massey University team calculated that the 187 measles cases confirmed during a 2014 outbreak cost $1.3 million in lost wages, hospital costs, public health management costs, and tracking down those who had come into contact with sick people. The researchers concluded that you could spend more than $10m on a catch-up programme - about $100 per person - and still save money in the long run.

To bring the costs of a programme down further, the research suggested targeting those who fall into the immunity gap. "High school aged children and young adults born in the late 1990s and early 2000s could be targeted, as beyond the young, these cohorts were least likely to be vaccinated and most likely to be [measles] cases," the research team wrote in Vaccine.

Despite the Ministry of Health funding and supporting the research, there is still no catch-up programme. "They were partners in this - there was a Ministry of Health employee as a co-author - and so they're fully aware of this," Hayman says. "I know that there has been a stakeholder meeting. But I'm not entirely sure exactly where that's gone after that - I don't actually know exactly how these decisions are made."

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The research has not been forgotten, ministry director of public health Caroline McElnay says. "Those papers are very useful papers, very informative, a lot of mathematical modelling, and some really interesting findings."

"It's certainly something that internally we are looking at… Taking more of a medium-term approach, is there something that we can do to address that immunity gap in those older age groups?" The ministry is still "pulling together information", though, and there is no timeline for a nationwide catch-up programme.

The ministry is interested in what is happening in Canterbury, where a public health campaign prompted by the current outbreak has targeted people aged between one and 28 years old. About 27,000 people have received an extra dose of measles vaccine as a result. "Quite a number of those people who were vaccinated were in the age group that we would want to target elsewhere in the country," McElnay says. "And they didn't necessarily have any of those [immunisation] records to be able to call people… I think that's what we need to have a much better understanding of, is what's the best approach."

Part of the success in Canterbury may be down to timing, she says. "That's in the midst of an outbreak… When you're not in the midst of an outbreak, how do you get that call to action and that response?"

There's another reason why a catch-up programme has been kept on the backburner. Since the Massey research was published, childhood immunisation rates have actually fallen by a small but significant margin; down from a high of 93 percent of two-year-olds in 2014 to 2016, to 92 percent in 2017, to 91 percent last year. The rate for the first three months of this year is also sitting at 91 percent. "I don't think we know why it's fallen back slightly, but we're very aware that it has fallen, particularly for some DHBs," McElnay says.

The trend is pronounced enough that the ministry has commissioned the Immunisation Advisory Centre to try to find out why, and what could be done to help DHBs lift their rates again. The childhood immunisation programme has to be the priority, she says. "While recognising that we've got a immunity gap in an older age group, actually, we still need to keep our focus and our attention on our immunisation schedule … [and] not creating a new immunity gap going forward."

The faint but long shadow of the MMR-autism link still hangs over some communities, along with other fears about vaccine safety, strengthened and amplified by word-of-mouth and online sources of misinformation. Cameron Edwards has seen that first-hand. "I've got a few of my mates who are anti-immunisation… It's that autism study that still hangs around. And I suppose their parents went through the same thing and didn't get them immunised, and they believe what their parents have told them, which is quite understandable. Because you only know the knowledge you get told."

"We are seeing a small increase, in some localised areas, of people who are questioning the science," Turner says. "They often go on social media and they get fed with a whole lot of very scary stories. And people get nervous and anxious for their children." As with previous periods of lower vaccination rates, though, the main hurdles are likely to be systemic. "Often it is hard for families to access immunisation services," she says. "We've got the potential to offer much more innovative approaches."

David Hayman says complacency may also play a role. "Part of the reason I think people are a little bit blasé about measles is that people have forgotten what it's like to have those sorts of diseases."

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It's not a disease that Edwards is ever likely to be blasé about. By the time he came home from hospital, he had lost 7kg. His immune system was shot to pieces and he immediately developed a pneumonia-like chest infection. He started going back to school after a month but every little bug laid him low and it took him a year to go back full-time. He didn't have the strength to play rugby, and the fledgling social groups that had been forming when he got sick had consolidated without him, leaving him isolated and frustrated. "I never really got back to normal with anything at high school."

Nowadays, he stands a foot taller than his mum and has just finished a horticulture course in Rotorua. Edwards-Lasenby says the two of them have discussed the choice she made two decades ago and her son understands "that the place that I came from was good". She still struggles to shake her "guilty mother's syndrome" though. "There's been long-reaching effects for him."

She knows from her own experience that parents have their children's best interests at heart. "But sometimes as you grow older things change, the environment changes, and there's consequences." A catch-up programme would give people who were not immunised as children - for whatever reason - a second chance. "As an adult, you can make your own choices about your health. And if you think that that's really important, then you can make that decision for yourself."