Canada is making strides against whooping cough in adolescents but must do more to prevent the illness in adults, according to an infectious diseases expert at Dalhousie University in Halifax.

Dr. Scott Halperin, a professor of pediatrics, microbiology and immunology, said most provinces and territories adopted a publicly funded vaccination program for adolescents in 2004-2005, and early reports suggest it's working.

Health officials hope to reverse a trend that has seen a higher incidence of whooping cough in adolescents in North America, Halperin said.

In 2003, the rising number of cases among teens and adults prompted a national advisory committee to recommend that all children and teenagers get a special shot that combined protection against tetanus and diphtheria.

The national advisory committee that established the adolescent program has also recommended one for adults. But Halperin said that hasn't happened and it's likely because of the cost.

Canada is lagging behind the U.S. on vaccinating adults against pertussis, the clinical name for whooping cough, Halperin said. Many American insurance companies and health-care institutions pay for the shot.

According to the Public Health Agency of Canada, in 1998 there were 8,910 cases and by 2004, that had decreased to 3,120 cases.

But the incidence of the disease among adolescents and adults started to rise in the 1990s, likely due to waning immunity, poor effectiveness of a previous vaccine and increased diagnosis.

In Canada in 1995, 9.6 per cent of cases were found in adolescents and adults, and that had risen to 31.3 per cent by 2004.

Halperin said adults can spread the disease to infants under six months. Babies can then suffer from complications, including seizures or even death.

Halperin said immunizing adults would also help protect children, who are much more likely to experience complications from the disease.

"Well over 50 per cent of cases in infants you can trace back that the source of that infection was the parent," Halperin says.

Dr. Stanley Read, an infectious diseases consultant at the Hospital for Sick Children in Toronto, said adults who don't stay up to date on their booster shots can help spread whooping cough.

"We end up with the possibility of a pool of potentially infectious organisms that could be prevented by vaccine occurring in adults who themselves have not kept their immunizations up to date," Read said.