In total, 1000 pregnant women were recruited, and 946 women were eligible to participate after the exclusion of 54 women (14 based on age or gestational age, 16 who miscarried, 3 who later refused to participate, 9 with duplicate information, 11 with missing or wrong information, and 1 no longer residing in Quebec).
Of these 946 women, 741 answered the second trimester survey and 568 of them, the third trimester survey. Table 1 presents participants’ characteristics according to vaccination uptake. The majority of participants were ≥ 30 years of age (60.9%), born in Canada (74.7%), French speaking (83.x%), married (90.5%), and had a university degree (57.5%). Almost half (46%) were in their first pregnancy (Table 1).
Overall, 82.4% of participants have been vaccinated against Tdap during pregnancy. Statistically significant differences were found in vaccine uptake according to country of birth (p = 0.004), first language (p = 0.004) and vaccination sites (P < 0.0001).
Determinants of participants’ intention to receive the Tdap vaccine during pregnancy
The internal reliability of the four components of the theoretical model was good. Cronbach’s alpha was between 0.62 and 0.87, with the exception of direct perception of control (0.57). In the second trimester, 76.3% of mothers had positive intentions regarding Tdap vaccination during pregnancy. Vaccine intention was correlated with positive attitude toward vaccine efficacy (α = 0.70), vaccine safety (α = 0.87), and vaccination in general (α = 0.87). Indirect perceived behavioral control (α = 0.83) and subjective norms (α = 0.80) were also correlated with the intention of taking the vaccine.
Results of the multivariate analysis for the second trimester survey are shown in Appendix 2. Subjective norms score, positive attitudes toward Tdap vaccine, perception of having enough information to make a decision on Tdap vaccination during pregnancy, low fear of adverse events, anticipated regret (or anticipated feeling of guilt if not taking the Tdap vaccine), easy access to Tdap vaccine during pregnancy and positive attitudes toward effectiveness of the vaccine were factors found to influence the intention to take the vaccine.
Determinants of participants’ receipt of the Tdap vaccine during pregnancy Of the 76,6% women who intended to be vaccinated against pertussis, 93.8% acted on their intention and received the vaccine. Of the 23.4% of women who did not intend to get the vaccine, 45.1% were vaccinated. Among women who intended to get the vaccine and were vaccinated, the main reasons for it were: having received a recommendation from a health care provider (83.6%), having had the opportunity to be vaccinated during a routine appointment (42.9%), and perception that Tdap vaccination is useful to protect their baby’s health (74.8%) (Table 2). Similar reasons were mentioned by women who did not intend to be vaccinated in the second trimester but took the vaccine.
Out of 76.6% women who had the intention of being vaccinated in the second trimester questionnaire, 6.2% did not receive the vaccine and of the 23.4% who had no intention of being vaccinated, 54.9% did not receive it either. The main reasons for not being vaccinated among women who did not intend to do so were: fear of adverse events of the Tdap vaccine during pregnancy (32.9%), thinking that the Tdap vaccine during pregnancy was not important (23.3%) and thinking that the Tdap vaccine was not useful for their babys’ health (15.1%) (Table 3). For women who intended to take the vaccine but did not take it, the main reasons were: difficulty to make an appointment to be vaccinated during pregnancy (18.5%), it was complicated to have the vaccine (11.1%), and other reasons (59.3%).
The majority of participants (95.5%) who received the vaccine had been informed by a health care provider about vaccination (85.5% by their own maternal care provider) (Appendix 3). In comparison, 63% of participants who were not vaccinated mentioned having been informed about Tdap vaccination in pregnancy (49% by their own maternal care provider). Written information about Tdap vaccination was given to 91.7% of women who were vaccinated compared to 69% of unvaccinated women. The main other sources of information reported by unvaccinated participants were: health care providers who don’t follow pregnancy. For vaccinated participants, these other sources were: someone who promoted the study at their clinic, friend, health care provider that they talked to during the pregnancy.
Results of the multivariate analysis on determinants of Tdap vaccine uptake are shown in Table 4. Recommendations from a healthcare provider(OR = 7.6), intention to be vaccinated(OR = 6.12), subjective norms(OR = 3.81), vaccination sites (in a general family medicine unit (OR = 3.63) and in an obstetric clinic (OR = 2.97)), perceived behavioural control (e.g., ease of access to vaccination services)(OR = 2.32) and anticipated regrets(OR = 2.13) were significantly correlated with Tdap vaccine uptake.