Impact de la vaccination sur l’épidémiologie des maladies infectieuses : exemple de la coqueluche

Abstract

Plusieurs vaccins ont maintenant été utilisés en routine depuis plus de cinquante ans dans certains pays. Leur impact a été de considérablement diminuer la morbidité et la mortalité liées à la maladie infectieuse qu’ils ciblent. Cependant, à long terme toutes ces maladies n’ont pas été éradiquées ni contrôlées. Cette variabilité est la conséquence de différents paramètres spécifiques à chaque maladie. Dans le cas de la coqueluche, le vaccin contenant des bactéries tuées a diminué la mortalité et la morbidité chez les nourrissons, mais a induit un changement de la transmission de la maladie. Ce changement a entraîné une modification de la stratégie vaccinale qui n’a pu être mise en place que grâce au développement de nouveaux vaccins ne contenant que quelques protéines bactériennes purifiées et inactivées.

Several vaccines are now routinely used since fifty years in different developed countries. Their principal impact has been to decrease morbidity and mortality of the infectious diseases they are targeting. One disease, smallpox, is eradicated, poliomyelitis will be soon, diphteria is controlled in several countries but pertussis is still endemic although an efficacious vaccine was used. Why ? Pertussis is an example of an infection for which the immunity of the population has changed after the introduction of generalized vaccination with killed whole cell pertussis vaccines, from a natural immunity due to infection to different types of vaccine-induced immunity. These different types of immunity have changed the protection against infection, disease and transmission. The impact of the generalized vaccination in a human population has been an important change in the epidemiology of the disease. In fact, a child-to-child transmission observed before the introduction of vaccination is now replaced by an adolescent-adult to infant transmission. The major consequence is an increase in the mortality and morbidity in non vaccinated infants mostly contaminated by their parents. Researches undertaken on the agent of the disease, the bacterium, Bordetella pertussis, conducted to the development of subunits vaccines, efficacious and better tolerated by infants than whole-cell vaccines. Many developed countries decided to change vaccines but also to add vaccine boosters for adolescents and adults in order to stop the transmission of the disease to infants. However, even after 15 years of studies in many countries, pertussis is still underestimated in adults and generalized adult vaccination remains difficult. The new goal now is to give information to medical students and health care workers in general in order to increase adolescent and adult’s vaccination coverage.