A new double-strain polio vaccine is more effective than triple and single vaccines and will be a potent weapon in the battle to eradicate the crippling virus, World Health Organisation (WHO) scientists said.

In a study in the journal the Lancet, WHO experts said a study on the bivalent oral polio vaccine, known as bOPV, found it induced a "significantly higher immune response" than triple vaccines.

This means that children in high-risk areas can be immunised against two key strains of the crippling virus with a single oral vaccine, said WHO scientist Roland Sutter, and the vaccine could "get us to the finish line of polio eradication".

The bivalent oral vaccine is made for WHO immunisation programmes by drug firms including Britain's GlaxoSmithKline  and India's Panacea Biotec.

"The main advantage of the bivalent is that it is so effective against type 1 and type 3 poliovirus at the same time," Sutter told Reuters in a telephone interview.

"The impact has been quite dramatic already in India and in Nigeria with cases coming down to very low levels this year.”

In a briefing after the study was published, WHO spokesman Rod Curtis said some 72 million children in 15 countries across Africa would be vaccinated in immunisation campaigns this week, including 55.7 million who will receive the bivalent vaccine.

"This will raise immunity to both types of polio so the chances of a significant outbreak are largely reduced," he told Reuters in Geneva.

Polio, which spreads in areas with poor sanitation, attacks the nervous system and can cause irreversible paralysis within hours of infection. Children under five are the most vulnerable.

In 1988, when the WHO and its partners formed the Global Polio Eradication Initiative to lead a drive to eradicate polio, the virus was endemic in 125 countries and paralysed nearly 1,000 children every day.

Dramatic reduction since 1988

Mass vaccination with older triple, or trivalent, oral polio vaccines has helped reduced the number of countries where polio is endemic to just four and there has been a 99 per cent reduction in polio cases worldwide since 1988.

Despite the use of these triple vaccines as well as monovalent, or single strain vaccines, polio virus types 1 and 3 are still circulating in the polio-endemic countries of Afghanistan, Pakistan, India, and Nigeria.

In their study, conducted between August and December 2008, Sutter's team analysed data from 830 babies in three centres in India who received the monovalent, bivalent or trivalent vaccines in two doses, one at birth and one at 30 days.

Blood samples were taken before vaccination and after the first and second doses to measure rises in antibody levels and the researchers found that, in targeting polio types 1 and 3, bOPV was better than both the triple and single vaccines.

In a commentary in the Lancet, Nigel Crawford and Jim Buttery from the Murdoch Children's Research Institute in Melbourne, Australia, said the potential effectiveness of the bivalent vaccine was already being shown in India where it is being used on a large scale. Latest polio data show just 32 cases so far this year, compared with 260 in 2009, they wrote.

But they said the global financial crisis had left a big gap in funding for immunisation programmes worldwide which must be closed if the aim of eradicating polio was to be achieved.

"The plan of action for polio eradication -- with bOPV as the centrepiece -- is only 50 per cent funded for 2010-12," they wrote, adding that "a final concerted effort, both locally and worldwide, is required" to eradicate the virus. – Reuters