Vaccination programmes are likely to eradicate the crippling polio virus around the globe within four years, health officials claimed on Thursday.
The virus has been targeted by the World Health Organisation’s eradication programme since 1988 and if eliminated will become only the second disease to be wiped out completely, after smallpox, which was officially declared eradicated in 1979.
Bruce Aylward at the WHO’s Global Polio Eradication Initiative said confidence had been boosted by research that identified ways of dislodging the virus from its last remaining strongholds. The virus is now endemic only in India, Nigeria, Pakistan and Afghanistan.
”We will not go into the next decade with polio,” Aylward predicted on Thursday.
Hopes of eliminating polio from the Uttar Pradesh and Bihar regions of India have been questioned following repeated infections that have triggered outbreaks in traditionally polio-free countries when sick people have travelled.
In research published in the journal Science on Friday, experts at Imperial College London reveal that the reason for polio’s persistence in India is a combination of the vaccine used and poor sanitary conditions leading to the spread of infections causing diarrhoea, which reduces the effectiveness of the vaccine.
The vaccine used widely in the polio eradication programme contains weakened versions of all three strains of the virus.
But the scientists found that when this so-called trivalent vaccine is injected one of the viral strains dominates and the body may become resistant only to that strain.
A study of 96 421 cases of paralysis caused by polio since 1997 revealed that one strain, Type 1 poliovirus, was far more likely to dominate than others.
The research has prompted the WHO to develop a new vaccine that gives resistance to Type 1 polio only, and efforts to introduce it are expected to begin early next year.
Poliomyelitis invades the nervous system and can cause total paralysis in a matter of hours. The virus multiplies in the intestine, causing fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs.
One in 200 infections leads to irreversible paralysis, usually in the legs. Among those paralysed up to 10% die when their breathing muscles fail.
”The global eradication programme has achieved a great deal. As expected the last remaining pockets of transmission are the biggest challenge,” said Nick Grassly, lead author of the paper.
”These pockets of transmission act as sources for all the outbreaks we see around the world today.
”Our research shows that in northern India the efficacy of the trivalent vaccine is compromised.
”Given that this same vaccine has achieved remarkable results in other parts of the world, this suggested there was biological interference with the vaccine.
”The new monovalent vaccine has potential to significantly boost immunity to the dominant poliovirus in these areas.”
Polio cases have fallen around 99% since 1988, from more than 350 000 cases in more than 125 endemic countries, to 1 951 reported cases in 2005.
This year Kenya reported its first case of polio in 22 years, the latest in Africa since hardline clerics in Nigeria ordered an immunisation boycott amid fears it was part of a US ploy to sterilise Muslims or infect them with the HIV virus. – Guardian Unlimited Â