Adverse events following diphtheria, pertussis and tetanus vaccinations and factors associated with severity

OBJECTIVE: To analyze adverse events following vaccinations against diphtheria, pertussis and tetanus (AEFV-DPT) and to investigate factors associated with event severity. METHODS: A cross-sectional study was carried out with a descriptive and analytical component covering AEFV-DPT that were notified in the State of Sao Paulo, Brazil, between 1984 and 2001, among children less than seven years old. Cases were defined as used in AEFV-DPT surveillance; the data source was AEFV-DPT passive surveillance. In calculating the rates, the numerator was the number of AEFV-DPT and as denominator was the number of doses applied. The association between severity of AEFV-DPT and the exposures of interest was investigated by means of non-adjusted and adjusted estimates of odds ratios, with their respective 95% confidence intervals, using non-conditional logistic regression. RESULTS: A total of 10,059 AEFV-DPT were identified, corresponding to 6,266 children who presented one or more AEFV-DPT, 29.5% were hospitalized and 68.2% presented contraindications for subsequent DPT doses. Around 75% of the events occurred during the first six hours after vaccination. The most frequent AEFV-DPT were: fever < 39.5 degrees C, local reactions, hypotonic-hyporesponsive episodes and convulsion. Time interval of less than one hour between vaccination and the event (OR = 2.1), first dose applied (OR = 5.8) and previous personal (OR = 2.2) and family (OR = 5.3) neurological histories were independently associated with severe events. CONCLUSIONS: Passive surveillance of AEFV-DPT was shown to be useful for monitoring the safety of the DPT vaccine, through describing the characteristics and magnitude of these events, and also enabling identification of possible factors associated with severe forms.