Ten people a week are falling ill with whooping cough as an outbreak continues to sweep across Sussex.
There have been 405 confirmed cases in the county so far this year, 13 times higher than the total for 2011.
Cases are mainly affecting children and adults but very young babies have also been infected.
Brighton and Hove has had 77 cases, while 144 and 184 have been recorded in East Sussex and West Sussex respectively.
At the end of September, the Department of Health announced pregnant women would be offered the whooping cough vaccination to protect their newborn babies, who are not usually vaccinated until they are between two and four months old.
The introduction of the vaccine programme in pregnant women will help to boost the short-term immunity passed on by women to their babies while they are still in the womb.
Mary Ramsay, the head of immunisation at the Health Protection Agency, said: “We have been very concerned about the continuing increase in whooping cough cases.
“All parents should ensure their children are vaccinated against whooping cough on time, even babies of women who’ve had the vaccine in pregnancy – this is to continue their baby’s protection through childhood.
“Parents should also be alert to the signs and symptoms of whooping cough – which include severe coughing fits accompanied by the characteristic “whoop” sound in young children but as a prolonged cough in older children or adults.