A "super-strain" of meningococcal disease that killed six people this year could become the dominant form in New Zealand if rates follow foreign trends, scientists say.
The Institute for Environmental Science and Research (ESR) began reporting every week on the group W meningococcal disease (MenW), after the number of cases jumped from five in 2016 to 24 this year.
GPs and emergency departments were asked to be aware of possible symptoms.
Fatalities included Alexis Albert, 7-year-old Whangarei, whose mother implored for a nationwide vaccination and awareness program, and 16-year-old Kerikeri, Dion Hodder, who died at Auckland City Hospital soon after falling ill on a Motutapu. youth camp.
Meningococcal disease is a bacterial infection that causes meningitis – an infection of the membranes surrounding the brain – and septicemia, or blood poisoning.
While meningococcal B (MenB) has been the dominant strain in New Zealand, causing two thirds of the cases of the disease, there have been growing concerns about the increase in MenW.
The proportion of MenB cases has dropped from 67% in 2017 to 49% in the year so far, while MenW rates have risen from 11% to 28%.
Dr Jill Sherwood, ESR's public health physician, said that the increase in the last two years was "significantly higher" than the annual average of notifications for 2012-2015, when only 2.5 cases were reported.
The strain was particularly troubling as it was more difficult to diagnose, much more virulent, and implicated in higher mortality rates – potentially up to 15% of cases.
It also affected a wider age group, with more than 40% of cases involving adults over 40 years.
Worryingly, it was possible that New Zealand was following trends observed in other countries, such as Australia, where MenW became the dominant strain in 2016.
"Although the number of MenW cases in New Zealand is still relatively low, there is a growing trend in notifications and a recent change in the type of sequence similar to the UK, Australia and Canada."
Whether or when MenW overtook MenB was difficult to predict, since case numbers were few, Sherwood said.
ESR monitored meningococcal disease looking for patterns based on basic demographics such as age, gender, ethnicity, location, living conditions, and start dates.
"For meningococcal disease, we also reviewed the type of group and type of stress and how many cases with the same strain and group that were not known to have close contact with each other occurred within specific populations in the last three months."
In the early 2000s, the government launched a national vaccination program following an outbreak of menB, but has since been withdrawn from the vaccination scheme.
However, the Government was now considering public funding of vaccines against the new strains of meningococcal disease – including MenW.
Associate Professor at the Immunology Advisory Center, Nikki Turner, said that New Zealand had vaccines for some high risk groups that could be purchased, but they were not on the national schedule.
"I am aware that our authorities have, and continue to think, about the introduction of these vaccines in New Zealand," Turner said.
"It's a bit complex and a lot of factors need to be weighed."
Turner noted that vaccines, while effective, did not give life-long protection.
"The disease occurs mostly in infants, younger children and adolescents and the body is usually carried in the throat of adolescents, but not exclusively," she said.
"Schedules that focus on these two ages are likely to be the most effective. We already have many vaccines in the children's calendar so adding others can be done, but it's not simple.
"Adolescents also need a dose, and we currently have a visit to the mid-age vaccination schedule, but not high school, which may be a better age to overcome the higher risk years of late adolescents before vaccine efficacy decreases . "
The other complex issue was the role of "herd immunity" – in which a largely immune population could help protect the few who were not.
"If we campaigned on all the young people, we could reduce the transport of the organism in people's throats and thus prevent further disease before introducing a vaccine into the schedule."
New Zealand was not the only country struggling with how best to manage the disease, she said.
"I think there's definitely a role for the vaccines here, but unfortunately they will not be a magic bullet."
By the numbers
The W Group's share of all cases of meningococcal disease this year – six of them fatal – rose from 11 percent last year.
49 percent: The proportion of the dominant group B cases this year, up from 67 percent last year.
15 percent: The potential proportion of MenW cases that are deadly.
40 percent: At least four out of 10 cases involve patients over the age of 40.