Why new polio cases have put the world on alert

Michael Toole

22/08/2022 5:22:04 PM

Professor Michael Toole explains what the resurgence means for Australia and people travelling overseas.

Child receiving oral polio vaccination.
Recent cases of polioviruses in the UK, US and are derived from the oral polio vaccine, which can lead recipients to excrete the virus in the stool for several weeks.

Until recently, polio had only been detected in a handful of countries, thanks to global eradication efforts.
But this year’s polio alerts in the United States, United Kingdom and Israel are a reminder that as long as poliovirus is found anywhere, it is a potential problem everywhere.
That could include Australia.
Here’s what the latest polio cases mean for Australia – including under-vaccinated communities and people travelling internationally.

The US case
In July this year, a young man in Rockland County, New York, developed paralysis and was diagnosed with polio, the first US case since 2013.
He had never been vaccinated against polio, which is not uncommon among Orthodox Jewish people in some countries. Rockland County has the highest percentage of Orthodox Jewish people in the US. Currently, only about 60% of children in the county are vaccinated against polio, compared with more than 90% nationally.
As of 12 August, poliovirus was still being detected in sewage in New York City and other counties in New York State, indicating the virus is still circulating in the community.
The reason there have been no further cases of paralysis reflects the fact that only around one in 200 people infected by the virus develops paralysis.
A child in Israel
One indirect link to the New York man may be in Jerusalem where, in March 2022, poliovirus was found in sewage and one case of paralysis occurred in an unvaccinated child.
Vaccination rates among Ultra-Orthodox Jewish people in Israel have been historically low, including low uptake of COVID vaccines. UK ramps up vaccination
In June this year, the UK Government reported wastewater surveillance in north and east London between February and May had identified poliovirus on consecutive occasions.
This indicated a provisional ‘silent’ outbreak and prompted health officials to instigate catch-up vaccination campaigns. No cases of paralysis have been reported. This is reminiscent of an earlier ‘silent’ outbreak of polio in 2013–2014 when, after decades without a case, Israel detected poliovirus in wastewater samples in many areas, mainly in southern regions.
Stool surveys indicated the outbreak was restricted mainly to children under the age of 10 in the Bedouin population of southern Israel. The virus originated in Pakistan and arrived in Israel via Cairo and then, probably, through Bedouin communities in Egypt and Israel.
Hang on, hasn’t polio been eradicated?
It’s tempting to think polio has been eradicated.
The last case of locally acquired polio in Australia was in 1972.
Australia was declared polio-free on 29 October, 2000, along with the other 36 countries in the Western Pacific Region of the World Health Organization. The last case reported in Australia was in 2007, when a student contracted the infection in Pakistan.
The Global Polio Eradication Initiative, launched in 1988, successfully eliminated wild poliovirus from all but two countries – Pakistan and Afghanistan – where in recent years there have been very few cases.
In Afghanistan, there were four cases last year and one so far this year. In Pakistan, there was one case in 2021 and 14 so far this year.
The recent cases and wastewater detected polioviruses in the UK, US and Israel are not the wild variety. Instead, they are derived from the oral polio vaccine.
When a child receives a dose of the oral vaccine, they excrete the virus in the stool for several weeks. In very rare cases, the vaccine-derived virus mutates to a form that causes paralysis.
This form is called a circulating vaccine-derived poliovirus (cVDPV). This occurs only in populations where polio vaccine coverage is low.
Just recently, cVDPV was reported in the Democratic Republic of the Congo, Mozambique and Yemen, as well as in wastewater in five other countries.
Australia, like all high-income countries, does not use the oral polio vaccine. Instead, children receive injectable inactivated polio vaccine, which prevents paralysis but does not prevent transmission of the virus.
This is why so-called silent outbreaks can occur in countries that use the injectable vaccine. This is when the virus spreads from child to child but does not cause paralysis.
What are the implications for Australia?
Given Australia’s open international borders, there is no reason why someone who has recently received the oral polio vaccine wouldn’t enter the country and excrete the virus.
In Australia, at the age of five, about 95% of children are fully vaccinated against polio.
However, there are places with lower vaccine coverage, such as Byron Shire in northern New South Wales, with lower rates of childhood vaccination, including against polio.
This vaccine-hesitant community is vulnerable to the introduction of polio and has had cases of diphtheria, whooping cough, measles and tetanus in recent years.  Unlike some other Orthodox Jewish communities overseas, there is no evidence this community in Australia is more vaccine hesitant than other Australians.
How do we look out for cases?
For years, wastewater monitoring has been routinely implemented in many countries. This acts as an early warning system to identify and rapidly mitigate the spread of many pathogens, including poliovirus, hepatitis viruses and, recently, SARS-CoV-2 (the virus that causes COVID).
At wastewater treatment facilities, sewage from an entire region is combined. This allows scientists to detect pathogens at the population level and before anyone presents with symptoms.
In December 2017, Victoria’s environmental testing program detected a rare type of poliovirus in pre-treated sewage from the Western Treatment Plant in Melbourne.
No cases of paralytic polio were detected but all Victorians up to the age of 19 were offered three doses of vaccine, free of charge, as part of catch-up arrangements.
Australia’s poliovirus infection outbreak response plan focuses on clinical surveillance (where health workers report suspected cases to health authorities) and laboratory investigations of people who present with acute paralysis.
While the plan refers to examples of wastewater surveillance overseas, it does not propose a specific strategy in Australia.
Other than Victoria, it is not clear where wastewater polio surveillance is being conducted in Australia.
What happens next?
Australia is just as vulnerable to importations of poliovirus – both wild and vaccine-derived – as any other country.
Australia should ensure routine wastewater surveillance for poliovirus is conducted, at least in metropolitan areas.
Community-based vaccination campaigns should be sensitively conducted in vaccine-hesitant communities, such as in Byron Shire, to achieve high coverage.
Education should also be provided through GPs to parents planning to travel to Jerusalem, New York City and Rockland County. They should ensure all travelling family members are fully vaccinated against polio.
Visitors to Israel may be able to access a dose of oral polio vaccine in that country for their children (which will prevent them being infected) but this is not available in the US.
Poliovirus enters the body through the mouth, usually from hands contaminated with the stool of an infected person. So parents should also pay special attention to their children’s hand hygiene, particularly if travelling overseas to any of the locations mentioned.
The article was originally published in The Conversation. Read the original article.
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