What predicts postpartum pertussis booster vaccination? A controlled intervention trial.

Background: 'Cocooning' aims to protect susceptible infants from pertussis via caregiver vaccination. Control trials evaluating educational interventions to promote cocooning are lacking. We evaluated the role of message-framing vs. standard health information in promoting pertussis vaccination.

Methods: We recruited postpartum women from a maternity hospital in Sydney, Australia (November 2010-July 2012). Participants self-completed a pertussis knowledge and attitudes questionnaire. We then assigned pertussis-susceptible (no pertussis vaccine ≤10 years) participants to receive a gain-framed, loss-framed pamphlet or control (Government Pertussis factsheet) using weekly sequential block allocation. Next, participants were offered a pertussis vaccine (dTpa) and completed a post-questionnaire on discharge.

Results: A baseline questionnaire was completed for 96.4% (1433/1486) of postpartum women approached. Missing data was excluded (n=29). Next, participants (1404) were screened for vaccine status: 324 (23%) reported prior pertussis booster vaccine receipt, leaving 1080 participants requiring vaccination. Among susceptible mothers, 70% (754/1080) were vaccinated post-intervention. Rates were similar between 'gain', 'loss' or 'control' pamphlets (69.1% vs. 71.8% vs. 68.8%; p=0.62). Intention to be vaccinated (OR 2.46, p<0.001; 95% CI: 1.69-3.58), perceived vaccine benefits (OR: 1.61, p<0.001; 95% CI: 1.25-2.15) and having received a vaccine recommendation (OR 1.68; p=0.025; 95% CI: 1.07-2.65) were independent predictors of vaccine uptake. At discharge, overall pertussis vaccine coverage had increased from 23% to 77% among women screened (1078/1404).

Conclusion: A cocooning strategy for pertussis vaccination can be highly effective when partially implemented within maternity hospitals, with information accompanied by a funded vaccine. Mothers were highly receptive to vaccination in the postnatal ward: facts about pertussis were as effective as message-framing in promoting a high uptake of 70%. Perceived vaccine benefits, intentions and vaccine recommendation were important predictors of uptake. Our intervention trial increased the existing pertussis vaccine coverage of 23-77%.