Using both types of polio vaccine could speed up efforts to free the world of the disease, research suggests.
The oral vaccine is leading the fight to eradicate polio, but trials in India show an additional injection of inactivated virus boosts immunity.
The World Health Organization said the findings, published in the journal Science, were “truly historic”.
The disease, which is spread through contaminated faeces, can cause paralysis and even death.
Fighting polio has been one of the biggest success stories in global health.
In 1988, there were 350,000 cases of polio in more than 125 countries.
The disease is now widespread in just three countries – Nigeria, Afghanistan and Pakistan – and cases have fallen by more than 99%.
Two drops of the oral vaccine, which contains a weakened polio virus, is the preferred tool in eradication efforts because it is cheap and gives resistance in the digestive tract to lower transmission of the virus.
The injected vaccine works largely in the bloodstream.
“But the oral vaccine is less effective in exactly those places we’d like it to work,” one of the researchers, Prof Nicholas Grassly, of Imperial College London, told the BBC.
It is thought other infections may interfere with the vaccine.
The solution has been multiple vaccination. As part of India’s successful eradication campaign, some children received 30 doses by the age of five.
Trials in India showed using an injection of inactivated virus as a booster jab was more effective than multiple drops.
However, the biggest challenge in banishing the disease for good is not the choice of vaccine, but getting to children in conflict-ridden areas.