The number of babies who have died in the biggest outbreak of whooping cough for 20 years has increased to 10, health officials said.
Ten infants under the age of three months have died in England so far this year as a result of the infectious disease.
There were 1,322 confirmed cases in England and Wales in September alone, 300 more than the total figure for 2011 when there were 1,118 cases, the Health Protection Agency (HPA) said.
In a move to combat the outbreak, health officials recently announced that all pregnant women are to be vaccinated against the infection.
Chief Medical Officer Professor Dame Sally Davies said mothers-to-be will be offered the vaccination to protect their newborn babies.
Youngsters cannot receive the jab until they are two months old. Vaccinating their mothers before they are born will boost their immunity until they reach the age they can get the injection themselves, she said.
Increases in whooping cough are usually seen every three to four years. The last rise in the number of confirmed cases was recorded in 2008.
The largest number of cases have been in those over the age of 15 but there has also been a sharp rise in whooping cough in babies aged under three months.
The cases have been spread across England and Wales, with the highest concentration in the south-east and south-west of England.
Dr Mary Ramsay, head of immunisation at the HPA, said: “The introduction of a vaccine for pregnant women will not have an immediate impact on serious infection in infants so vigilance remains important.
“All parents should ensure their children are vaccinated against whooping cough on time, even babies of women who have had the vaccine in pregnancy – this is to continue their baby’s protection through childhood.”