The Department of Health announced a new £10m vaccination programme for 650,000 pregnant women to protect their infants once they are born, while they are too young to be immunised themselves.

There have been nine deaths in England of babies under the age of ten weeks and one in Northern Ireland, the highest number of deaths for a decade. None had been vaccinated before they fell ill.

Newborn babies cannot mount an immune response to vaccines so experts said the best way to protect them is to give their mothers a booster late in pregnancy so that her antibodies against the disease are passed to the unborn child.

It is only the second time pregnant women will be routinely offered a vaccine while pregnant, after the pandemic flu vaccine and then the seasonal flu jab following the H1N1 swine flu outbreak.

Women are generally advised not to take any medication that is not absolutely necessary while pregnant but experts said the seriousness of the outbreak and the safety of the vaccine made this the most effective option.