Trends and characteristics of Tdap vaccination during pregnancy in Ontario, Canada: a retrospective cohort study

Abstract

Background: In February 2018, Canada's National Advisory Committee on Immunization (NACI) recommended tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccination during pregnancy to protect newborns against pertussis infection. We sought to describe pre- and postrecommendation trends in Tdap vaccination coverage among pregnant Ontario residents.

Methods: Using linked health administrative databases, we conducted a population-based retrospective cohort study of all pregnant individuals who gave birth in Ontario hospitals between April 2012 and March 2020. We described Tdap vaccination patterns in pregnancy for the entire study period and before and after the NACI recommendation. We used log-binomial regression to identify characteristics associated with Tdap vaccination during pregnancy.

Results: Among the 991 850 deliveries included, 7.0% of pregnant individuals received the Tdap vaccination during pregnancy. Vaccine coverage increased from 0.4% in 2011/12 to 29.2% in 2019/20. Coverage was highest among individuals who were older, had no previous live births, had adequate prenatal care and received maternity care primarily from a family physician. After adjustment, characteristics associated with lower coverage included younger maternal age, having a multiple birth, residing in a rural location and higher area material deprivation. In 2019/20, 71.0% of vaccinated individuals received the Tdap vaccination during the recommended gestational window (27-32 wk). Stratified analyses of the pre- and postrecommendation cohorts yielded similar findings to the main analyses with a few gradient differences after adjustment.

Interpretation: During pregnancy, Tdap vaccination coverage increased substantially in Ontario between 2011/12 and 2019/20, most notably after recommendations for universal Tdap vaccination during pregnancy began in Canada. To further improve vaccine coverage in the obstetric setting, public health strategies should consider tailoring their programs to reach subpopulations with lower vaccine coverage.

Figure 1:

Study flow diagram. Note: CIHI = Canadian Institute for Health Information, DAD = Discharge Abstract Database, OHIP = Ontario Health Insurance Plan, Tdap = tetanus toxoid, reduced diphtheria toxoid and acellular pertussis.

Figure 2:

Tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccination coverage by fiscal year of conception. The dotted line indicates the fiscal year in which Canadian recommendations for routine Tdap vaccination during pregnancy were released (February 2018).

Figure 3:

Gestational timing of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccination overall and by fiscal year of conception. (A) Bar graph presenting the distribution of gestational age at which Tdap vaccination was received during pregnancy. (B) Box plot presenting the median gestational age at which Tdap vaccination was received during pregnancy (horizontal line within each box plot) and the interquartile range (vertical lines extending above and below each box).