A partial dose of polio vaccine was as good as a full one in providing a basic level of immunity against the crippling disease, according to a study that may offer poor countries a cheap, effective way of ensuring the disease doesn’t return after it’s eradicated in an area.
In a trial among 310 babies in Cuba, a one-fifth-sized dose of the shot primed the immune systems of 94 percent of the infants for poliovirus type 2, compared with 98 percent of those who received a full dose, researchers at the World Health Organization wrote in the New England Journal of Medicine today. That means their systems are ready to pump out protective antibodies on receipt of a second dose, which would be given if polio were to re-emerge.
The WHO, backed by the Bill and Melinda Gates Foundation, is nearing a global goal of eradicating polio, which has been cleared from every country except Afghanistan, Nigeria and Pakistan. Today’s findings support the Geneva-based agency’s efforts to maintain a basic level of immunity in case the disease returns.
“We were almost blown away by the level of priming that we saw after a single dose,” said Roland Sutter, a WHO researcher who participated in the trial. “We did not expect that we would see this at this level,” Sutter said in a telephone interview.
After two doses of the partial vaccine, 98 percent of the infants were protected against type 2 polio, compared with 100 percent of those who got the regular dose, the researchers found.
Polio, which mainly affects children under five years, is caused by a virus that invades the nervous system and can cause irreversible paralysis within hours. Vaccination campaigns have reduced the number of cases by more than 99 percent to about 650 in 2011 from about 350,000 in 1988, according to the WHO.
In preparation for the post-eradication phase of the campaign, the WHO has recommended that countries include at least one dose of polio vaccine in their routine childhood immunization program. The agency has also recommended that countries switch to the injected polio vaccine, which contains a dead form of the virus, from the commonly used oral vaccine, which contains a disabled live form that in rare cases has led to cases of polio.
The trial, which was funded by the WHO and the Pan American Health Organization, suggests that giving two one-fifth doses of the vaccine could reduce the cost of protecting a child to $1.20 from $6 now, the researchers wrote. A single priming dose would cost 60 cents, they said.
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