LONDON (Reuters) -- A new double-strain polio vaccine is more effective than triple and single vaccines and means children in high-risk areas can be immunized against two key strains of the crippling virus in a single dose, scientists say.

In a study in the Lancet journal on Tuesday, World Health Organization (WHO) scientists said research on the bivalent oral polio vaccine, known as bOPV, found it induced a “significantly higher immune response” than triple vaccines.
Researcher Roland Sutter said the findings showed that the new oral vaccine, which is made for WHO vaccination programs by various drug firms including Britain's GlaxoSmithKline and India's Panacea Biotec, would be a potent weapon in the battle to eradicate the crippling virus.
The “main advantage of the bivalent is that it is so effective against type 1 and type 3 poliovirus at the same time,” he 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.”
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 paralyzed nearly 1,000 children every day.
Mass vaccination with older triple, or trivalent, oral polio vaccines have helped reduced the number of countries where polio is endemic to just four. But 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 and colleagues analyzed data from 830 newborn babies from three centers in India who received either the monovalent, bivalent or trivalent vaccines in two doses, one at birth and one 30 days later.
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 polo data show just 32 cases so far this year, compared with 260 in 2009, they wrote.