Protection against whooping cough, also known as pertussis, appears to wane a few years after immunization with pertussis vaccine during infancy. Therefore, booster vaccination is probably warranted at 5 to 7 years of age, doctors from Sweden conclude in a report in the journal Pediatrics.

Pertussis is a bacterial infection characterized by cough lasting 14 days or longer accompanied by a gasping sound or “whoop” while coughing. Before the advent of the pertussis vaccine in the late 1940s, pertussis was a major cause of illness and death, especially among infants and young children.

Dr. Patrick Olin, from the Swedish Institute for Infectious Disease Control in Solna, and colleagues assessed the long-term efficacy of pertussis vaccines given at 3, 5, and 12 months of age. The study included 90 percent of Swedish children who were born in 1996 or later and children who were enrolled in large pertussis vaccine trial between 1993 and 1996.

As uptake of pertussis vaccines increased during the 1990s, the rates of confirmed pertussis fell, the team reports. For instance, the number of confirmed cases per 100,000 person-years was 113 to 150 from 1992 to 1995 compared with just 11 to 16 in 2001 to 2004.

There was also evidence that pertussis cases fell with a full infant immunization schedule. With administration of all three doses rather than just two, the incidence of pertussis fell from 31 to 19 cases per 100,000 person-years.

The incidence of pertussis following the third vaccine dose held fairly steady until 6 to 8 years of age when it jumped up to 32 to 48 cases per 100,000 person-years.

“Our observations support the introduction of a booster dose of pertussis vaccines around school entry, already introduced in several countries, and suggested in Sweden at around 6 years of age,” the authors conclude.

The study was funded in part by GlaxoSmithKline and Sanofi Pasteur, both makers of pertussis vaccines.

SOURCE: Pediatrics September 2006.