[Epidemiological estimation of the effectiveness of the pertussis vaccination during outbreaks in a community. Les pédiatres et bactériologistes du réseau RENACOQ].

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.