WASHINGTON – New research suggests a one-two punch could help battle polio in some of the world’s more remote and strife-torn regions: Giving a single vaccine shot to children who’ve already swallowed drops of an oral polio vaccine greatly boosted their immunity.
“It could play a major role in completing the job of polio eradication once and for all,” said Dr. Hamid Jafari, WHO’s director of polio operations, who led the study published Thursday in the journal Science.
Oral polio vaccine has played a critical role in the nearly three-decade effort to eradicate the paralyzing disease, as health workers have gone house-to-house, to refugee camps and to roadside checkpoints delivering the drops.
Which vaccine to use in the eradication push has long been controversial. They each have different strengths. The United States and other wealthy countries have switched back to using only injected polio vaccine, which is made of “inactivated” or killed virus, for routine childhood immunizations. That’s because the oral vaccine contains weakened live virus that children can shed in their stools, which on very rare occasions can trigger a vaccine-caused case of polio.
In developing countries where polio is still a threat, the oral version is cheaper, easier to use and can slow spread of the virus. But a particular type of immunity, intestinal immunity, wanes so that children in high-exposure areas need repeated doses.
Jafari’s team tested whether using both vaccines would protect better than one. The study involved nearly 1,000 children, from babies to 10 year olds, in northern India in 2011, the last year that country reported a case of polio. The children previously had received oral vaccine. This time, they randomly were assigned to receive either a dose of injected polio vaccine, another oral dose or no booster. Four weeks later they all received what researchers called a “challenge” dose of oral vaccine to see how their bodies shed the weakened live virus.
The shots acted as a better booster for the children’s intestinal immunity than giving them yet more vaccine drops – and those youngsters shed far less virus, key to cutting transmission in an outbreak, Jafari’s team reported.
And in December, Kenya put the strategy to its first real-world test. Health workers used both injected and oral vaccine as they sought to immunize 126,000 young children living in Somali refugee camps and nearby areas who were at risk from a polio outbreak spilling over the Somalia-Kenya border.
Similar campaigns are beginning in northeastern Nigeria and should start soon in Pakistan, said Jafari and Dr. Bruce Aylward, WHO’s assistant director-general for polio.
The injected vaccine is more expensive, Aylward said – about $1 to $1.90 a shot, compared to about 15 cents a dose for oral vaccine. But he said it was worth the investment if adding the shots wound up eliminating polio in the last infected areas faster.
Using this strategy in these tough-to-reach areas makes sense, CDC vaccine expert Dr. Steve Cochi said.
At the same time, the WHO has called on low- and middle-income countries that now use only oral polio vaccine to add one dose of the injected version to routine childhood immunizations next year.