Most of us think of polio as a disease consigned to the past, or isolated in developing countries.
In fact, the virus is only currently endemic in two countries – Afghanistan and Pakistan.
But recently a young unvaccinated man in Rockland County, New York, was paralysed by polio and is the first person to be infected in the United States in nearly a decade.
The case in New York is genetically linked to those found in both Jerusalem and London.
Health officials have since found virus fragments in New York City’s wastewater and say the detection suggests there is local transmission.
In early August, Britain’s health agency confirmed the virus is spreading in London for the first time since the 1980s, after first finding it in wastewater in June.
The States wasn’t previously looking for polio in wastewater whereas the UK had been, epidemiologist at University of Otago Peter McIntyre told Kim Hill.
“All of a sudden when this case emerged, they’ve started looking and they’ve found that they’ve got a problem.”
There are three types of the polio virus, and the current cases in New York and London are all type 2 – an oral vaccine-derived strain.
Polio can spread by coughing, sneezing or sharing drink bottles as well as by contact with the faeces of an infected person through things such as not washing your hands properly after going to the toilet or by changing baby nappies, the Ministry of Health says.
So how did this happen?
It all comes back to the World Health Organization's polio endgame strategy, which started in 2013 with the aim of eradicating polio, says McIntyre.
“That campaign has hit a few humps on the road.
“I guess in a rush of enthusiasm following the disappearance of type 2 it was decided to take that strain, the type 2 strain, out of the oral polio vaccine.”
While most developed nations use an injected vaccine made up of dead virus, the oral vaccine is still used by many developing countries and is made up of live but weakened virus.
The weakened virus used in the oral vaccine can cause polio in about 1 in 750,000 cases, according to the Ministry of Health.
McIntyre says taking the type 2 strain out of the oral vaccine seemed like a great idea, because if you only had two strains in the vaccine you got better responses.
But change doesn’t happen overnight and, in the meantime, the virus was spreading, giving more time for it to mutate, he says.
“So the type 2 vaccine strain, which was still around actually, was able to mutate and turn into something which could cause paralysis again. And so we’ve been chasing our tail since then, because there have been a series of outbreaks of the vaccine-derived strain."
The idea was for people who had an oral vaccine to also get one dose of the injected vaccine - the one New Zealand has been using since 2002.
New Zealand began immunising with the oral polio vaccine in 1961 but in 2002 an inactivated polio vaccine was introduced because it can’t cause illness.
Unfortunately, McIntyre says, many countries didn’t have great coverage of the vaccine.
“We’ve had great success in terms of getting rid of wild polio, just before Covid we were getting down to really only a couple of countries with only a few cases but in the meantime, these vaccine-derived strain two paralysis cases have been burgeoning.”
WHO had plans to withdraw the oral vaccine from use when polio nears global elimination.
Should we be worried about cases showing up here in New Zealand?
World Health Organization spokesperson for polio eradication Oliver Rosenbauer earlier told Morning Report polio is a threat to countries everywhere around the world.
Someone is infectious for about six to eight weeks and may not have symptoms so could spread the virus while travelling.
“The only way to protect yourself until the disease is fully eradicated is to make sure that you have strong surveillance...and to make sure that your population is fully vaccinated so that the virus doesn’t have a chance to take a foothold.”
New Zealand and Australia both undertake a type of polio surveillance, looking for acute flaccid paralysis cases, says McIntyre.
“If you get a child where they suddenly develop a floppy paralysis of their legs or arms, then the idea is that if you test all of those cases for polio virus, you’ll make sure you’re not getting polio back.
“In somewhere like New Zealand, all of those cases turn out to be something else.”
In fact, we haven’t had a case of polio here since 1998.
But, like elsewhere around the world, there has been a disruption in routine childhood vaccinations during the Covid-19 pandemic.
Immunisation coverage at six months of age has fallen in New Zealand from a high of around 80 percent in early 2020 to 67 percent by June 2022, and as low as 45 percent for Māori.
“But we’re still in good shape and the injectable vaccine works extremely well. The thing it doesn’t do so well is it doesn’t give you immunity in the gut so if a polio virus did turn up then the inactivated vaccine isn’t nearly as good at sorting that out.
“It’s not a problem we’ve got at the moment.”
With cases showing up in London, the UK has launched a campaign to get children in London an extra booster dose of the vaccine - McIntyre doesn’t think New Zealand is at that stage yet.
“These diseases are very well controlled because we’ve got high vaccination rates and the thing about successful vaccine campaigns is that we know they’re successful because nothing happens – we don’t have cases, we don’t have adverse effects from vaccines.”
McIntyre says polio and measles are both reminders that when we take our eyes off the ball, these diseases don’t go away.
Most people who encounter the virus don’t have any symptoms, he says.
“The fact that this 20-year-old guy developed paralysis means there must have been thousands, possibly many thousands of people who’d been infected by the virus that we didn’t know about.
“He is the tip of a very large iceberg.”