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The re-emergence of polio
Polio, a disease once thought to be well controlled through immunisation, is now re-emerging around the globe.
Dr Joan Ingram, medical advisor at the Immunisation Advisory Centre at The University of Auckland, explains why.
"The polio virus has affected humans since Egyptian times. In the first half of the century it caused numerous feared outbreaks in New Zealand, leading to paralysis and disability for thousands. Today, a disease once thought to be well controlled through immunisation, is re-emerging around the globe.
"The introduction of polio vaccinations in the 1950s achieved a remarkable end to the outbreaks. Dr Neil Begg, the medical director of Plunket at the time said: “It is doubtful if future physicians will feel greater elation and relief than we did when we found that the killing, deforming, the terrifying disease of polio had been banished by effective immunisation."
"Unfortunately, 60 years later the disease continues to spread globally so here in New Zealand we must maintain good polio vaccination coverage to prevent recurrence of infections and possible cases of paralysis."
No place is safe until polio has been eradicated everywhere. As long as the virus still exists somewhere in the world, it can spread – including in our own country.
"Only humans are susceptible to poliovirus infection and alongside the availability of very effective vaccinations, in 1988 the WHO adopted a resolution for the global eradication of polio. The world had achieved smallpox eradication and polio was our next target.
"Since then, reported polio cases dropped by 99.9%. In 2020 the African region was declared polio free and only Pakistan and Afghanistan continued to have wild polio infections.
"Unfortunately, over the past two years wild polio has remerged in Malawi and Mozambique and there have been outbreaks of vaccine derived polio cases in over 20 countries."
The race to vaccinate everyone | "The oral vaccine widely used overseas which is cheap, highly effective and easy to administer multiplies in the intestine and is shed in the bowel motions of those vaccinated. In rare cases it can mutate while living in a person’s intestine and revert to a version of the virus that can cause poliomyelitis (it is for that reason that New Zealand changed in 2002 from the oral polio vaccine to the injectable one). The mutated vaccine virus does not cause complications in people who have already previously been vaccinated, but if an unvaccinated person swallows it, they may develop paralytic polio as happened in an unvaccinated person in New York recently.
"While there continue to be any polio cases (either wild or vaccine-derived) in the world, it is important that polio vaccination coverage remains high as travel allows the arrival of people shedding the virus.
"It’s the reverse of the old saying, “it's gone, but not forgotten,” Schaffner, an American doctor recently said. "Polio is forgotten, but it's not gone.""
Want to know more? | If you or your children need polio vaccination talk to your family doctor. A primary course of poliomyelitis vaccine is usually given at ages six weeks, three months and five months, followed by a booster dose given at age four years. For partially immunised or previously unimmunised older people, a course consists of three doses of vaccine and is funded.
For more information, visit The Immunisation Advisory Centre's website.