One-fifth of British school-age children who visit their doctors because of a persistent cough are diagnosed with whooping cough, according to a new study.
What's more, most of the children have been fully vaccinated, the study authors reported.
"Pertussis [whooping cough] can still be found in a fifth of school-age children who present in primary care with persistent cough and can cause clinically significant cough in fully vaccinated children," Kay Wang, of the University of Oxford, and colleagues wrote in the study published online on June 24 in BMJ.
Read: Whooping cough making a comeback
The researchers looked at 279 children, aged 5 to 15, who were seen by their family doctor about a cough that had lasted two to eight weeks.
Tests showed that 20 percent of the children had evidence of recent whooping cough infection, including 18 percent who had been fully vaccinated against the disease.
Children who'd received the preschool pertussis booster vaccination more than seven years ago were three times more likely to have pertussis than those who received the booster more recently. The risk of pertussis was similar for children who received either a three or five component preschool booster vaccine.
Read: Whooping cough cases reach record high
Children in the United Kingdom receive pertussis vaccinations at 2, 3 and 4 months of age, with another preschool pertussis booster vaccination three years after completing the initial course, according to background information in the study.
Before the preschool pertussis booster shot was introduced in the United Kingdom in 2001, nearly 40 percent of school-age children with persistent cough were found to have whooping cough.
"These findings will help to inform consideration of the need for an adolescent pertussis booster vaccination in the United Kingdom," the authors concluded.
Whooping cough vaccine protection wanes
Irregular vaccination increases whooping cough risk
Whooping cough vaccines fades in pre-teens