Moderna said it would seek emergency use authorisation for its Covid-19 vaccine for children under the age of six in the US and EU in coming weeks after interim results from its clinical trial showed the jab is safe and produces a positive immune response.

But the results from the late-stage study released on Wednesday by the US drugmaker show the child-sized jab — about a quarter the size of an adult dose — was only modestly effective at preventing infection with the Omicron variant.

The vaccine was 43.7 per cent effective at preventing infection in children aged six months to two years and 37.5 per cent effective in preventing infection in children aged two to under six — a result that Moderna said was consistent with data from clinical trials in adults.