ABSTRACT
BACKGROUND: With the recent pertussis vaccine trials, the efficacy of acellular vaccines is now well known, estimated at 85% for multicomponent vaccines. On the other hand, the estimates of whole cell vaccines efficacy varies from 36% to 98% with the different vaccines used. We evaluated the field effectiveness of the French whole cell pertussis vaccine during outbreaks in schools and centers for disabled children. METHODS: Four limited outbreaks between 1993 and 1995 were investigated using a retrospective cohort study design. Vaccine effectiveness (VE) was assessed for the following case definition: clinical pertussis, laboratory-confirmed pertussis, epidemiologically confirmed pertussis (documented contact with a laboratory confirmed case). Immunization history was obtained by reviewing the child health record book. Effectiveness of a whole vaccination (four injections) and of a partial vaccination (one to three injections) were estimated as 1-(attack rate among vaccinated/attack rate among non-vaccinated). RESULTS: A whole immunization conferred good protection against pertussis with an estimated VE higher than 92% in three surveys, lower in the fourth survey (84%) in which antibiotic prophylaxis was set up very rapidly. A partial immunization conferred a mild protection (median: 60%). CONCLUSIONS: These results are consistent with a previous report about the effectiveness of this whole cell vaccine using the screening method in a hospital network survey in France. In the same way, a large efficacy trial in Senegal comparing it with an acellular bivalent vaccine estimated its efficacy at 96%. This high efficacy together with a satisfactory vaccine coverage leads to the current epidemiological profile of pertussis in childhood in France: majority of cases occurring before 6 months of age, limited outbreaks in school children, many of whom being unvaccinated or partially vaccinated.