Risk factors for acellular and whole-cell pertussis vaccine failure in Senegalese children.

Although use of acellular pertussis vaccine was associated with a higher rate of vaccine failure than that of whole-cell vaccine in the Senegal Pertussis Trial conducted in 1990-1994 on 4189 children, risk factors for vaccine failure regarding exposure and susceptibility to pertussis have not been studied so far. Pertussis occurred in 346 vaccinated children. Three factors were found to be associated with vaccine failure, independently of the vaccine type, namely the degree of exposure, birth rank, and time since weaning. In the whole-cell vaccine group, the risk of failure increased with birth rank [RR = 2.95 (1.51-5.75)] and was higher in non stunted children [RR = 1.43 (1.05-1.94)]. In the acellular vaccine group, the risk of failure increased with age at exposure to B. pertussis [RR = 2.24 (1.21-4.12) after 18 months of age] and the degree of exposure [RR = 2.14 (1.17-3.93) when the child shared the hut of an index case]. These results highlight the influence of environmental factors on the success of pertussis vaccination. However, they do not explain the shorter duration of protection provided by the acellular vaccine compared to the whole-cell vaccine which persist after controlling and thus might be related to the nature of the vaccine.