Giving just one-fifth the usual dose of the polio vaccine may protect babies against the virus nearly as well as a full dose, as long as it is injected just beneath the skin, doctors reported on Wednesday in the New England Journal of Medicine.
The findings could bring down the cost of immunization, an important consideration in developing countries, some of which have had trouble containing the paralytic disease.
A needle-free jet injector made by Bioject Medical Technologies was used to deliver the vaccine beneath the skin at ages 2, 4 and 6 months. Blood tests showed more than 95 percent of the infants mounted an effective immune response against polio.
Babies who got a lower dose had fewer antibodies against polio but the researchers said that should not be a problem.
"It's still way over what would still be considered protective levels," study author Dr. Roland Sutter of the World Health Organization said in a telephone interview.
The injectable vaccine costs about $3 per dose. The oral polio vaccine is much cheaper, at about 15 cents, but it contains a weakened virus that can mutate and sometimes cause polio in patients or when it gets into sewage.
So public health experts now favor the injectable vaccine.
"With this study, we know we can use this means to lower the price," Sutter said. "If we can do one-fifth the dose, we can at least get it down to one dollar, so we are getting into the neighborhood of a price that may be affordable for developing countries in the future."
Polio continues to be common in Afghanistan, India, Pakistan and Nigeria, sometimes because of war, sometimes because of overcrowding, Dr. John Modlin of Dartmouth Medical School in New Hampshire wrote in a commentary.
The big problem in Nigeria, Africa's most populous nation, was a one-year ban on the vaccine in some northern states, beginning in 2003, after some state governors and religious leaders in the predominately Muslim north claimed Western powers had contaminated the vaccines to spread sterility and AIDS among Muslims.
The study of 373 children was done in Oman, in part because there was little risk that natural polio would influence the results, Sutter said.
While just 4.3 percent of parents said they preferred needle vaccination for their child, 93 percent said they liked the needle-free method better, usually because the baby did not cry.
Polio, which spreads in areas with poor sanitation, attacks the nervous system and can cause irreversible paralysis within hours of infection. Children under 4 are the most vulnerable to the disease that until the 1950s crippled thousands of people every year in rich nations.
The World Health Organization has suggested a budget of $2.6 billion for its polio eradication efforts in 2010-2012, but says it faces a shortfall of about half of funds for that period.