For decades scientists have debated whether injectable or oral polio vaccine is the best option for trying to finish the job of eradicating polio. Now a new study offers an answer: Both.

The research, published today in the journal Science, says using at least one dose of the more expensive injectable vaccine after children have been vaccinated with the oral serum should speed up eradication and make the process safer.

The researchers suggest that giving the injectable vaccine after the oral boosts the immunity in a child's gut better than additional doses of oral vaccine, making them less vulnerable to circulating polio viruses.

The injectable vaccine is the type Canada and most developed countries have used for years.

It is safer, but significantly more expensive, and it has to be administered by a medical professional; oral vaccine drops can be given by trained volunteers.

The community of researchers and public health organizations working on polio eradication have argued for years whether OPV, as the oral vaccine is called, can get the job done in the developing world.

The injectable vaccine, called IPV, has had both fierce proponents and steadfast opponents — the latter objecting to its high cost, the need to buy and safely discard mass numbers of syringes and other complications.

The new study, by scientists from India and from the Global Polio Eradication Initiative, looked at the response of previously vaccinated (with OPV) Indian children who received a booster dose of OPV, IPV or a placebo.

They found the children who received IPV got the best boost to their immune response to the virus.

"Our study provides strong evidence that IPV boosts intestinal immunity among children with a history of multiple OPV doses more effectively than an additional OPV dose," the authors wrote.

That is important because it is believed the virus enters the body and initiates infection via the gut.

Cost concerns for polio shots

The World Health Organization has already changed its policy on polio vaccine and is no longer recommending an all-OPV approach for countries which until now have used only the oral vaccine.

It now recommends that countries that have been using OPV only introduce at least one dose of the injectable vaccine into their routine childhood vaccination schedules — a move which will come at a considerable cost for these nations.

OPV costs pennies a dose to buy and administer. Through dogged negotiations with vaccine manufacturers, UNICEF has gotten an agreement from producers that they will sell IPV for $1 US a dose to the poorest countries and $1.90 US a dose to middle-income countries.

UNICEF is one of the original partners in the polio eradication effort; the others are the service club Rotary International, the U.S. Centers for Disease Prevention and Control and the WHO. In later years, the Bill and Melinda Gates Foundation have become major players in the campaign.

The effort to eradicate polio began in 1988 with a target of making the world free of the disease by the start of the new millennium. But the virus has proved to be a much more difficult foe than smallpox, the only human pathogen to have been eradicated. (Rinderpest, a virus that afflicted cattle and other ungulates, was declared eradicated in 2011.)

Polio remains endemic — transmission has never been stopped — in three countries: Pakistan, Afghanistan and Nigeria. And viruses from those countries occasionally reignite spread in neighbouring countries or countries with trade or travel ties.

So far this year there have been 146 confirmed cases of polio in nine countries in Africa, the Middle East and South Asia. Most of the cases — 115 — have been reported in Pakistan, where political instability and religious resistance in the part of the country bordering Afghanistan have led experts to label the country the biggest threat to eradication.