The trivalent oral polio vaccine that produces immunity in the gut being administered in Afghanistan. Photo courtesy of the Global Polio Eradication Initiative.
Burnet Institute Deputy Director (International Program Strategy), Professor Mike Toole AM writes for The Conversation about the recent polio outbreak in Syria.
Here is an exerpt from the article.
As if the children of Syria had not suffered enough, the news of an outbreak of polio (poliomyelitis) signals that even more suffering lies ahead. The polio virus invades the nervous system and can kill or cause lifelong paralysis.
Wild poliovirus had not been detected in Syria since 1999. But on 17 October a cluster of 22 cases of “acute flaccid paralysis”, the signature symptom of clinical polio, was reported from Deir Al Zour province.
Since then, wild poliovirus type 1 (WPV1) has been found in ten of the cases under investigation, all in children under the age of two years.
The world has come tantalisingly close to eradicating polio. In the 1980s, the virus killed or paralysed around 350,000 people annually. Then Rotary International launched a global vaccination campaign, in partnership with the World Health Organization and UNICEF and more recently, the US Centers for Disease Control and Prevention and the Bill and Melinda Gates Foundation.
In 2012, there were just 223 cases in five countries. Only three countries – Afghanistan, Nigeria and Pakistan – have never interrupted transmission of the wild poliovirus.
But this year, there have been severe setbacks in the endeavour to eradicate a human disease for just the second time in history – the first being smallpox.
In Somalia, 180 cases of polio have been reported so far this year in areas controlled by the Islamic militants Al Shabab, which has banned vaccination. That outbreak has spilled into neighbouring countries with 14 cases in Kenya and seven in Ethiopia.
Worldwide, there have already been 332 cases this year – almost 50% higher than last year’s total.
Types of vaccinations
There are three types of wild poliovirus: 1, 2, and 3. There have been no cases of WPV2 since 1999 and the last case of WPV3 occurred in Nigeria almost 12 months ago. All cases of polio this year have been caused by WPV1. In theory, this trend makes it easier to control the disease.
The most commonly used vaccine is trivalent oral polio vaccine (OPV) which produces immunity in the mucosa (soft tissue) of the gut to all three types, preventing the virus from entering the bloodstream. But newly developed monovalent vaccines more efficiently induce immunity against a single type.
The downside is that on rare occasions the live vaccine virus mutates into a paralytic form, is excreted from the gut, and may circulate in communities where immunity is low. This is called circulating vaccine-derived poliomyelitis and is the reason why most developed countries such as Australia have switched to inactivated polio vaccine (IPV). This injectable vaccine induces immunity in the bloodstream but not in the gut.
CLICK HERE to read the full article.
Professor Toole is a member of the Independent Monitoring Board of the Global Polio Eradication Initiative.