Parental Tdap boosters and infant pertussis: a case-control study

Area of Science:

• Public Health
• Epidemiology
• Vaccinology

Background:

• Pertussis (whooping cough) prevention strategies, including cocooning, lack robust field effectiveness data.
• A government-funded cocoon program during a pertussis epidemic in New South Wales, Australia, was evaluated.

Purpose of the Study:

• To assess the effectiveness of vaccinating close adult contacts of newborn infants against pertussis.
• To evaluate the impact of a cocoon program on pertussis incidence in infants.

Main Methods:

• Laboratory-confirmed pertussis cases in infants <4 months were matched with controls from the birth register.
• Parental vaccination status was self-reported, with a subset verified; immunization was defined as vaccination ≥4 weeks before case symptom onset.
• Vaccine effectiveness was calculated as (1 - odds ratio) × 100%.

Main Results:

• Households with pertussis cases had lower rates of immunized mothers (22%) and fathers (20%) compared to controls (32% and 31%, respectively).
• When both parents were immunized, the risk of pertussis in infants <4 months was reduced by 51% (95% CI: 10% to 73%).
• Maternal vaccination prepregnancy and paternal immunization independently reduced pertussis risk by 51% (95% CI: 0% to 76%).

Conclusions:

• Timely parental pertussis booster vaccinations offer significant protection to infants.
• Evidence supports the protective effect of maternal vaccination prepregnancy, warranting further research into its magnitude and duration for policy development.