There were 3,523 confirmed cases of pertussis in the first seven months of 2012, more than three times more than in 2011, when 1,118 cases were reported.
There were 235 cases reported in infants under three months up to the end of July, and six pertussis-related deaths in infants.
The HPA said that young infants are at highest risk of severe complications and death from whooping cough because babies do not gain benefits from vaccination until they are around four months old.
The UK is currently experiencing the largest surge of pertussis since the early 1990s, with cases running well above the most recent surge in cases in 2008.
Confirmed pertussis cases
Dr Gayatri Amirthalingam, an expert in immunisation at the HPA, said the agency was ‘very concerned’ about the continuing increase in cases.
‘Parents should ensure that their children are vaccinated on time so that they are protected at the earliest opportunity and be alert to the signs and symptoms – which include severe coughing fits accompanied by the characteristic "whoop" sound in young children but as a prolonged cough in older children or adults,’ Dr Amirthalingam said.
‘We also advise parents to keep their babies away from older siblings or adults who have the infection.’
Dr Amirthalingam added: ‘GPs have also been reminded to report cases quickly and been made aware of the HPA’s guidance to help reduce the spread of infection – this improved awareness may be contributing to the increase in numbers of laboratory confirmed cases.’
The Joint Committee on Vaccination and Immunisation has said that GP immunisation clinics may need to be overhauled to help stem falling immunity against pertussis.
The committee has also suggested that GPs should clear waiting lists, recommend earlier jabs in some circumstances and examine changes to practice IT systems to eliminate delays in vaccinating young children.