Effectiveness of the pertussis vaccination program as determined by use of the screening method: United States, 1992-1994.

The screening method was used to evaluate the effectiveness of the pertussis vaccination program in the United States during 1992-1994. The formula VE = 1 - [PCV/(1 - PCV)][(1 - PPV)/PPV] was used (VE = vaccine effectiveness; PCV = proportion of cases vaccinated; PPV = proportion of population vaccinated). Data from the national Supplementary Pertussis Surveillance System and the National Health Interview Survey were used to determine PCV and PPV, respectively. Among children aged 7-18 months, VE for 3 doses of pertussis vaccine was 79% (95% confidence interval, 74%-83%) for preventing culture-confirmed pertussis. Between the ages of 19 and 47 months, VE for > or = 4 doses was 90% (95% confidence interval, 88%-92%). VE estimates appeared lower in epidemic (1993) than non-epidemic years (1992, 1994). VE estimates determined using the screening method were consistent with the previous estimates from the United States. This method will continue to be useful for assessing the effectiveness of the pertussis vaccination program in the United States, where acellular pertussis vaccines are recommended for infants.