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Pertussis Vaccination in Canadian Pregnant Women, 2018–2019

Open AccessPublished:February 09, 2022DOI:https://doi.org/10.1016/j.jogc.2022.01.014

      Abstract

      Objective

      This study was undertaken to measure the uptake of pertussis vaccination during pregnancy in Canada and to identify sociodemographic factors associated with non-vaccination.

      Methods

      A total of 5091 biological mothers of children born between September 2, 2018, and March 1, 2019, were interviewed about pertussis vaccination during their pregnancy.

      Results

      Among 4607 mothers who recalled whether they had been vaccinated for pertussis, 43% had been vaccinated and 57% had not. The main reason given by mothers for not having been vaccinated was not being aware that pertussis vaccination was recommended. Factors independently associated with non-vaccination were being born outside Canada, lower household income, living in a province or territory where pertussis vaccination was not provided free of charge, having had previous live births, and having received maternity care from a midwife.

      Conclusion

      Advice from the maternity care provider is an important driver of pertussis vaccination during pregnancy.

      Résumé

      Objectif

      Cette étude a été entreprise pour mesurer la vaccination contre la coqueluche pendant la grossesse au Canada et pour identifier les facteurs sociodémographiques associés à la non-vaccination.

      Méthodologie

      Les mères biologiques de 5 091 enfants nés du 2 septembre 2018 au 1er mars 2019 ont été interviewées au sujet de leur vaccination contre la coqueluche pendant leur grossesse.

      Résultats

      Des 4 607 mères qui se souvenaient si elles avaient été vaccinées contre la coqueluche, 43% l’avaient été et 57% ne l’avaient pas été. La principale raison donnée par les mères de ne pas s’être fait vacciner étaient qu’elles ne savaient pas que c'était recommandé. Les facteurs indépendamment associés à la non-vaccination étaient : être née à l’extérieur du Canada, avoir un revenu du ménage plus faible, vivre dans une province ou un territoire où le vaccin n’était pas offert gratuitement, avoir eu d’autres naissances vivantes auparavant et avoir reçu son suivi de grossesse d’une sage-femme.

      Conclusion

      Les conseils du professionnel de la santé qui fait le suivi de grossesse influencent grandement la vaccination pendant la grossesse.

      Keywords

      Introduction

      Despite widespread vaccination, pertussis remains endemic in Canada,
      • Smith T.
      • Rotondo J.
      • Desai S.
      • et al.
      Pertussis surveillance in Canada: trends to 2012.
      ,
      Public Health Agency of Canada
      Vaccine preventable disease: surveillance report to December 31, 2017.
      with incidence rates highest for infants aged <1 year: 72.5 per 100 000 population from 2013 to 2017. The 4 pertussis-related deaths reported in Canada during this period occurred in infants aged <6 months.
      Public Health Agency of Canada
      Vaccine preventable disease: surveillance report to December 31, 2017.
      Vaccination with the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine during pregnancy induces the production of antibodies that are transferred through the placenta to the foetus and persist in infants up to 2–4 months of age.
      • Vilajeliu A.
      • Ferrer L.
      • Munrós J.
      • et al.
      Pertussis vaccination during pregnancy: antibody persistence in infants.
      ,
      • Halperin S.A.
      • Langley J.M.
      • Ye L.
      • et al.
      A randomized controlled trial of the safety and immunogenicity of tetanus, diphtheria, and acellular pertussis vaccine immunization during pregnancy and subsequent infant immune response.
      Maternal vaccination with Tdap has been shown to significantly reduce the incidence of pertussis in infants’ first 2 months of life,
      • Dabrera G.
      • Amirthalingam G.
      • Andrews N.
      • et al.
      A case-control study to estimate the effectiveness of maternal pertussis vaccination in protecting newborn infants in England and Wales, 2012-2013.
      • Skoff T.H.
      • Blain A.E.
      • Watt J.
      • et al.
      Impact of the US maternal tetanus, diphtheria, and acellular pertussis vaccination program on preventing pertussis in infants <2 months of age: a case-control evaluation.
      • Winter K.
      • Nickell S.
      • Powell M.
      • et al.
      Effectiveness of prenatal versus postpartum tetanus, diphtheria, and acellular pertussis vaccination in preventing infant pertussis.
      with administration of the vaccine during the third trimester of pregnancy being significantly more effective than vaccination during the second trimester.
      • Winter K.
      • Nickell S.
      • Powell M.
      • et al.
      Effectiveness of prenatal versus postpartum tetanus, diphtheria, and acellular pertussis vaccination in preventing infant pertussis.
      Tdap vaccination during the second or third trimester of pregnancy is not associated with any adverse pregnancy or birth outcomes.
      • McMillan M.
      • Clarke M.
      • Parrella A.
      • et al.
      Safety of tetanus, diphtheria, and pertussis vaccination during pregnancy: a systematic review.
      For these reasons, the National Advisory Committee on Immunization recommended in February 2018 that Tdap be administered in every pregnancy in Canada, ideally between 27 and 32 weeks of gestation.
      Update on immunization in pregnancy with tetanus toxoid, reduced diphtheria toxoid and reduced acellular pertussis (Tdap) vaccine. an Advisory Committee Statement (ACS) - National Advisory Committee on Immunization (NACI).
      In March 2018, the Society of Obstetricians and Gynaecologists of Canada issued a new clinical practice guideline on immunization in pregnancy that included a recommendation that every pregnant woman be offered Tdap, ideally between 21 and 32 weeks.
      • Castillo E.
      • Poliquin V.
      SOGC Clinical Practice Guideline no. 357 - immunization in pregnancy.
      As of November 2019, all provinces and territories except for Ontario and British Columbia had implemented programs to provide pertussis vaccination free of charge to pregnant women. Uptake of this newly recommended vaccination has yet to be analyzed for Canadian mothers.
      Because maternal vaccination for pertussis is relatively new, pregnant women and even health care providers may not be aware of it. In the United Kingdom in 2017–2018 (i.e., 5 years after the implementation of maternal vaccination against pertussis), there were still women declining vaccination because they feared it might harm their unborn child, and some maternity care providers were reluctant to discuss maternal vaccination with their patients.
      • Wilcox C.R.
      • Calvert A.
      • Metz J.
      • et al.
      Determinants of influenza and pertussis vaccination uptake in pregnancy: a multicenter questionnaire study of pregnant women and healthcare professionals.
      This study was undertaken to measure the uptake of pertussis vaccination during pregnancy in Canada and to identify sociodemographic factors associated with nonvaccination.

      Methods

      The Survey on Vaccination during Pregnancy was conducted for the first time as part of the 2019 Childhood National Immunization Coverage Survey. The survey collected information about prenatal care; pertussis and influenza vaccination during pregnancy; knowledge, attitudes, and beliefs regarding vaccination; and sociodemographic factors. A detailed description of survey methods and the questionnaire are available elsewhere.
      Statistics Canada
      Childhood national immunization coverage survey; 2020.
      A sample of babies born between September 2, 2018, and March 1, 2019, was selected randomly from the list of children for whom the Canadian Child Benefit was claimed, which was estimated to include 96% of Canadian children in 2018.
      Data were collected from December 2, 2019, to March 6, 2020 (i.e., 9–18 months after the selected child was born). The biological mothers of these children were contacted and invited to participate in the survey, provided they had lived in Canada for most of their pregnancy. Household income was provided from administrative data sources and was imputed when missing using the nearest neighbour method (0.1% of records).
      Estimation with nearest neighbour imputation at Statistics Canada. Proceedings of the Survey Research Methods Section, American Statistical Association 1999:131-138.
      For the purpose of assessing survey results, provinces and territories were grouped based on whether they were offering Tdap free of charge to pregnant women as of August 2018 (the month before new mothers were eligible for inclusion in the survey). The Northwest Territories, Nunavut, Saskatchewan, Québec, New Brunswick, and Prince Edward Island were all offering the Tdap vaccine free of charge to pregnant women at this time, whereas Yukon, British Columbia, Alberta, Manitoba, Ontario, Nova Scotia, and Newfoundland and Labrador were not.

      Ethics and Privacy

      This survey was conducted by Statistics Canada as part of its mandate to “collect, compile, analyze, abstract, and publish statistical information relating to the commercial, industrial, financial, social, economic, and general activities and conditions of the people of Canada” and was not therefore considered health research. The survey was completed on a voluntary basis, and data were kept confidential.

      Data Analysis

      Frequencies and percentages for all categorical variables were computed to describe the study sample. Weighted proportions with their 95% confidence intervals were also estimated using the modified Wilson method for the confidence limits. The association between sociodemographic factors and nonvaccination was measured using simple and multiple logistic regression models from which odds ratios and associated 95% confidence intervals were calculated. Although being advised to get vaccinated for pertussis was strongly associated with the mother being vaccinated in the simple regression model, this variable was not included in multiple regression because it was deemed to be an intermediate step in causal pathways between other factors and nonvaccination. Finally, because the variable describing the availability of Tdap vaccination free of charge was derived from the province or territory of care, these variables could not be included together in a model. Therefore, only the former was included, because it was deemed to be more informative given the objective of the study.
      With the exception of the unweighted rates in the sample description shown in Table 1, all rates and odds ratios described in this study were weighted using survey weights provided by Statistics Canada to ensure that estimates were representative of the population. To account for the complex survey design, standard errors and confidence intervals of weighted rates and odds ratios were estimated with the bootstrap technique.
      • Rust K.F.
      • Rao J.N.K.
      Variance estimation for complex surveys using replication techniques.
      Statistical analysis was performed using SAS version 9.4.
      Table 1Sample characteristics (n = 5091)
      VariableUnweighted, no (%)
      Columns may not add to the total sample size due to missing data.
      Weighted, % (95% CI)
      Mother’s country of birth
       Canada3852 (75.7)67.3 (65.4–69.2)
       Other1233 (24.2)32.5 (30.6–34.5)
      Mother’s age at childbirth, y
       15–271178 (23.1)22.4 (20.8–24.2)
       28–311525 (30.0)26.9 (25.2–28.7)
       32–341142 (22.4)22.5 (20.8–24.3)
       35–521195 (23.5)26.8 (25.0–28.7)
      Mother’s education
       Secondary or less1266 (24.9)26.0 (24.3–27.8)
       Postsecondary1467 (28.8)28.9 (27.1–30.8)
       University graduate2335 (45.9)44.4 (42.5–46.4)
      Household income, CAD$
       $0–$49 999984 (19.3)24.5 (22.9–26.2)
       $50 000–$89 9991366 (26.8)28.0 (26.3–29.8)
       $90 000–$129 9991185 (23.3)21.4 (19.9–22.9)
       $130 000 or more1556 (30.6)26.1 (24.6–27.5)
      Number of past live births
       02208 (43.4)42.5 (40.6–44.5)
       11861 (36.6)35.6 (33.7–37.5)
       ≥21019 (20.0)21.9 (20.3–23.7)
      Duration of pregnancy, wk
       <3272 (1.4)1.5 (1.0–2.2)
       32–36371 (7.3)8.2 (7.1–9.5)
       ≥374624 (90.8)89.7 (88.2–90.9)
      Primary maternity care provider during pregnancy
      May or may not be the professional who attended the child’s birth.
       Obstetrician/gynaecologist2957 (58.1)62.3 (60.4–64.1)
       General practitioner (family doctor)1472 (28.9)22.7 (21.2–24.2)
       Midwife442 (8.7)12.3 (11.0–13.6)
       Nurse116 (2.3)1.2 (0.9–1.6)
       Other or no maternity care101 (2.0)1.5 (1.1–2.1)
      Primary maternity care provider advised getting pertussis vaccine during pregnancy
       Yes2775 (54.5)49.2 (47.1–51.3)
       No1696 (33.3)37.4 (35.4–39.4)
       No maternity care (question not asked)15 (0.3)0.2 (0.1–0.5)
      Vaccinated for pertussis during pregnancy
       Yes2347 (46.1)39.1 (37.2–41.0)
       No2260 (44.4)50.8 (48.8–52.8)
       Don't know484 (9.5)10.1 (8.9–11.4)
      a Columns may not add to the total sample size due to missing data.
      b May or may not be the professional who attended the child’s birth.

      Results

      Of 9096 child/mother pairs selected from the sampling frame, 5091 completed the survey, yielding a response rate of 58.9% after removing out of scope cases. Respondent characteristics are described in Table 1. Of the mothers who participated in the survey, 39% reported having been vaccinated against pertussis during their pregnancy, 51% had not been vaccinated, and 10% did not know. Among women who recalled whether they had been vaccinated, the percentages of vaccinated and nonvaccinated mothers were 43% and 57%, respectively.
      Nearly all mothers (99%) had received maternity care during their pregnancy, mostly from obstetrician/gynaecologists (62%). There were no significant differences among women who had received maternity care from obstetrician/gynaecologists, family doctors, nurses, or midwives with respect to advice to get vaccinated for pertussis during pregnancy (Table 2). More women were advised to get vaccinated in provinces or territories where Tdap was provided free of charge to pregnant women (68%) than in provinces and territories where vaccination was not funded (52%).
      Table 2Association between maternal care provider and lack of advice to get vaccinated for pertussis during pregnancy
      OR: odds ratio; Tdap: tetanus, diphtheria, and acellular pertussis.
      VariableNo.Mothers not advised to get vaccinated for pertussis during pregnancy
      % (95% CI)Unadjusted OR (95% CI)
      Primary maternity care provider
      May or may not be the professional who attended the child’s birth. Mothers who received maternity care from an “other” professional or no maternal care at all were excluded from this analysis.
       Obstetrician/gynaecologist264442.8 (40.0–45.7)1.04 (0.84–1.28)
       General practitioner (family doctor)129941.9 (37.9–46.0)Reference
       Midwife35145.7 (39.2–52.4)1.17 (0.85–1.61)
       Nurse10134.8 (20.4–52.7)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      0.74 (0.32–1.70)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      Tdap during pregnancy
      Variable derived from the province or territory of care.
       Free of charge177731.5 (28.3–35.0)Reference
       Not free of charge261847.9 (45.1–50.7)2.00 (1.65–2.41)
      Note: Counts (no.) are unweighted; percentages and ORs are weighted.
      a May or may not be the professional who attended the child’s birth. Mothers who received maternity care from an “other” professional or no maternal care at all were excluded from this analysis.
      b Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      c Variable derived from the province or territory of care.
      The main reasons given by mothers for nonvaccination were not being aware that pertussis vaccination was recommended during pregnancy (60%), not wanting to be vaccinated during pregnancy (16%), and the vaccine not being offered by their maternity care provider (11%) (Table 3).
      Table 3Reasons reported by mothers for not getting vaccinated for pertussis during pregnancy (n = 2258)
      Rates are weighted; respondents could provide more than 1 answer.
      ReasonPercentage (95% CI)
      Not aware it was recommended59.6 (56.7–62.4)
      Did not want to be vaccinated15.9 (14.0–18.1)
      Not confident vaccine would protect baby3.0 (2.1–4.1)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      Could have harmed baby3.3 (2.5–4.4)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      Not offered by health care provider10.7 (9.1–12.5)
      a Rates are weighted; respondents could provide more than 1 answer.
      b Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      The rate of nonvaccination was significantly higher in provinces and territories where the vaccine was not offered free of charge (61%) than in those where it was publicly funded (46%). Other factors significantly associated with nonvaccination in simple logistic regression analyses were being born outside of Canada; lower education; lower household income; having had previous pregnancies; having had previous live births; having received maternity care from an obstetrician/gynaecologist or a midwife or having no professional care at all (compared with a family doctor); and not having been advised to get the vaccine (Table 4).
      Table 4Determinants of pertussis nonvaccination during pregnancy
      Tdap: tetanus, diphtheria, and acellular pertussis.
      VariableNo.
      The n values are unweighted. Percentages and odds ratios are weighted.
      ,
      “Not stated” categories are not shown, but were nevertheless included in the simple and multiple regression models, except for “mother's place of birth” (n = 5) and “number of past live births” (n = 1), the small sizes of which caused a problem of nonconvergence in the multiple regression model. The final multiple regression model includes 2344 vaccinated mothers and 2257 unvaccinated mothers (total 4601).
      Unvaccinated, % (95% CI)Odds ratio (95% CI)
      UnadjustedAdjusted
      Odds ratios are adjusted for all variables shown in the table, plus mothers' indigenous identity, age at childbirth, education, marital status, urban or rural area of residence, and duration of pregnancy.
      Mother’s country of birth
       Canada353153.0 (50.5–55.5)ReferenceReference
       Other107163.9 (59.9–67.7)1.57 (1.29–1.91)1.43 (1.15–1.79)
      Household income, CAD$
       $0–$49 99987457.1 (51.8–62.3)1.37 (1.05–1.78)1.16 (0.83–1.61)
       $50 000–$89 999123163.7 (59.7–67.5)1.80 (1.44–2.25)1.67 (1.29–2.17)
       $90 000–$129 999106555.3 (50.9–59.6)1.27 (1.01–1.60)1.26 (0.98–1.62)
       $130 000 or more143749.4 (45.7–53.0)ReferenceReference
      Province or territory where maternal care was received (or delivery if no maternal care received)
       Newfoundland and Labrador37784.1 (80.0–87.4)16.86 (11.28–25.21)
       Prince Edward Island29423.8 (19.3–29.1)Reference
       Nova Scotia42237.8 (32.8–43.1)1.94 (1.35–2.80)
       New Brunswick43529.0 (24.7–33.7)1.31 (0.91–1.87)
       Québec56851.2 (46.9–55.6)3.36 (2.41–4.67)
       Ontario50259.7 (55.1–64.1)4.73 (3.35–6.67)
       Manitoba39243.0 (37.6–48.5)2.41 (1.68–3.44)
       Saskatchewan43626.0 (21.7–30.8)1.12 (0.78–1.62)
       Alberta53862.1 (57.6–66.4)5.24 (3.75–7.31)
       British Columbia47474.4 (70.1–78.4)9.30 (6.48–13.34)
       Yukon, Northwest Territories, and Nunavut16929.9 (32.4–55.2)1.36 (0.64–2.89)
      Tdap during pregnancy (based on province of care)
      The “Tdap during pregnancy” variable is derived from the province or territory of care. Therefore, the latter was excluded from the multiple regression analysis.
       Free at each pregnancy183345.7 (42.3–49.3)ReferenceReference
       Not free at each pregnancy277461.3 (58.6–63.8)1.88 (1.57–2.25)1.78 (1.47–2.16)
      No. of past live births
       0203849.4 (46.2–52.6)ReferenceReference
       1166259.1 (55.4–62.6)1.48 (1.22–1.79)1.56 (1.27–1.92)
       ≥290666.8 (62.2–71.0)2.06 (1.62–2.61)2.14 (1.65–2.77)
      Primary maternity care provider during pregnancy
      “Maternity care provider” and “advice to get vaccinated” were not included together in a multiple regression because advice is an intermediate step in the causal pathway between provider and vaccination.
      ,
      May or may not be the professional who attended the child’s birth.
       Obstetrician/gynaecologist271455.8 (53.0–58.6)1.24 (1.01–1.52)1.15 (0.92–1.43)
       General practitioner (family doctor)131850.5 (46.4–54.5)Reference
       Midwife38570.4 (64.2–76.0)2.34 (1.68–3.26)2.21 (1.56–3.14)
       Nurse9747.9 (32.1–64.1)
      “Maternity care provider” and “advice to get vaccinated” were not included together in a multiple regression because advice is an intermediate step in the causal pathway between provider and vaccination.
      0.90 (0.44–1.87)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      0.84 (0.40–1.80)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
       Other/no maternal care9172.4 (57.2–83.7)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      2.57 (1.24–5.33)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      2.43 (1.12–5.30)
      Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      Primary maternity care provider advised getting pertussis vaccine during pregnancy
      “Maternity care provider” and “advice to get vaccinated” were not included together in a multiple regression because advice is an intermediate step in the causal pathway between provider and vaccination.
       Yes265721.7 (19.3–24.3)Reference
       No161795.3 (93.7–96.5)73.27 (51.40–104.46)
      Note: Only mothers who reported having been vaccinated (n = 2347) or not having been vaccinated (n = 2260) for pertussis during their pregnancy are included in this analysis. Those who did not know if they had been vaccinated are excluded. Only variables significantly associated with nonvaccination are shown in the table.
      a The n values are unweighted. Percentages and odds ratios are weighted.
      b “Not stated” categories are not shown, but were nevertheless included in the simple and multiple regression models, except for “mother's place of birth” (n = 5) and “number of past live births” (n = 1), the small sizes of which caused a problem of nonconvergence in the multiple regression model. The final multiple regression model includes 2344 vaccinated mothers and 2257 unvaccinated mothers (total 4601).
      c Odds ratios are adjusted for all variables shown in the table, plus mothers' indigenous identity, age at childbirth, education, marital status, urban or rural area of residence, and duration of pregnancy.
      d The “Tdap during pregnancy” variable is derived from the province or territory of care. Therefore, the latter was excluded from the multiple regression analysis.
      e “Maternity care provider” and “advice to get vaccinated” were not included together in a multiple regression because advice is an intermediate step in the causal pathway between provider and vaccination.
      f May or may not be the professional who attended the child’s birth.
      g Estimates and CIs are considered to be of marginal quality due to high sampling variability and should be used with caution.
      In multiple regressions, factors independently associated with nonvaccination were being born outside of Canada; household income between CAD $50 000 and $89 999 (compared with CAD >$130 000); having received maternity care in a province or territory where the vaccine was not offered free of charge; having 1 or more past live births; and having received maternity care from a midwife.

      Discussion

      Less than half of mothers had been vaccinated against pertussis during their pregnancy. Higher coverage rates have been reported in other countries with pertussis vaccination during pregnancy: 54% in the United States in 2018
      • Kahn K.E.
      • Black C.L.
      • Ding H.
      • et al.
      Influenza and Tdap vaccination coverage among pregnant women - United States, April 2018.
      ; 56% in England in 2014–2015
      • Byrne L.
      • Ward C.
      • White J.M.
      • et al.
      Predictors of coverage of the national maternal pertussis and infant rotavirus vaccination programmes in England.
      ; and 69% in Flanders (Belgium) in 2016.
      • Maertens K.
      • Braeckman T.
      • Blaizot S.
      • et al.
      Coverage of recommended vaccines during pregnancy in Flanders, Belgium. Fairly good but can we do better?.
      It is important to note that these measurements were taken a number of years after the vaccine was first recommended in each of these countries.
      In contrast, this survey was conducted the year after the issuance of new guidelines for vaccination during pregnancy in 2018, and some provinces and territories were not yet providing the vaccine free of charge. It might be expected that coverage rates will increase with time, as more provinces and territories fund the vaccine and the vaccine recommendation becomes more well known.
      Being advised by the primary maternity care provider was found to be the main driver of maternal vaccination. Consistent with that observation, being unaware that pertussis vaccination during pregnancy was recommended was the number one reason mothers gave for not being vaccinated. Maternity care provider practice was not investigated in this study. The vaccine being offered free of charge was clearly a determinant of advice from the maternity care provider but is not the sole explanation; one-third of mothers were not advised to get vaccinated in provinces where it was offered free of charge, and half were advised to get vaccinated in provinces and territories where the vaccine was not free. Of note, less than 1% of unvaccinated mothers mentioned the cost of the vaccine as the reason for nonvaccination.
      Socioeconomic inequalities observed in this study are consistent with observations from other countries. In the United States, in univariate analyses, vaccination rates varied with ethnicity and were lower in women with lower education, single women, those unemployed, those with public (vs. private) insurance, and those below the poverty line. Coverage was significantly lower in women who had only been advised to get the vaccine than in those who had been offered vaccination by a health care provider, and was even lower in those who had received no recommendation.
      • Kahn K.E.
      • Black C.L.
      • Ding H.
      • et al.
      Influenza and Tdap vaccination coverage among pregnant women - United States, April 2018.
      In England, coverage decreased with increasing deprivation.
      • Byrne L.
      • Ward C.
      • White J.M.
      • et al.
      Predictors of coverage of the national maternal pertussis and infant rotavirus vaccination programmes in England.
      Similarly, in Ireland, vaccine uptake decreased with decreasing socioeconomic status.
      • Quattrocchi A.
      • Mereckienen J.
      • Fitzgerald M.
      • et al.
      Determinants of influenza and pertussis vaccine uptake in pregnant women in Ireland: a cross-sectional survey in 2017/18 influenza season.
      In Belgium, it varied between income categories with no clear dose-response trend.
      • Maertens K.
      • Braeckman T.
      • Blaizot S.
      • et al.
      Coverage of recommended vaccines during pregnancy in Flanders, Belgium. Fairly good but can we do better?.
      Lower vaccination rates in adults born outside of Canada is consistent with what was observed in the Canadian Community Health Survey in 2011–2014, where seasonal influenza vaccination coverage was significantly lower for immigrants than for Canadian-born respondents.
      • Roy M.
      • Sherrard L.
      • Dubé È.
      • et al.
      Determinants of non-vaccination against seasonal influenza.
      It is also consistent with the 2006 Maternity Experiences Survey that found a lower uptake of some maternal health interventions, such as attending prenatal classes and taking folic acid, in immigrant women.
      • Kingston D.
      • Heaman M.
      • Chalmers B.
      • et al.
      Comparison of maternity experiences of Canadian-born and recent and non-recent immigrant women: findings from the Canadian Maternity Experiences Survey.
      Although the risk of nonvaccination varied depending on the primary maternal providers, and mothers followed by midwives were more likely not to get vaccinated, it is important to note that this does not imply a causal relationship. Mothers who decide to seek care from a midwife rather than from a medical doctor or a nurse may be already more reluctant about vaccination.
      Multiparous mothers may be less receptive to vaccination advice from health care providers than nulliparous ones, as prior personal experience of raising a healthy baby without having received pertussis vaccination during pregnancy might dampen motivation to accept a new intervention during subsequent pregnancies. Moreover, if the vaccine is not easily accessible, childcare may present barriers to uptake of vaccination even when multiparous mothers are accepting of the recommendation.
      This study was able to measure inequalities in uptake, but is not able to fully explain them. Further research to identify the underlying barriers and facilitators of maternal pertussis vaccination are needed.
      This study has strengths and limitations. The major strengths were a random selection (making it representative of the population) and a large sample size (more than 5000 mothers, of whom more than 4600 could be included in coverage estimations). Limitations include self-reporting of vaccination, which may have led to recall bias or social desirability bias. There may also have been nonresponse bias, as survey mothers who agreed to participate in the survey may have been different from those who did not. However, this bias would have affected the actual coverage estimates, not the associations observed in the study between maternity care, sociodemographic variables, and nonvaccination.

      Conclusion

      Despite guidelines, half of the mothers surveyed had not been vaccinated for pertussis during their pregnancy. Advice from the maternity care provider is an important driver of pertussis vaccination during pregnancy.

      Acknowledgements

      The authors are grateful to all survey participants and to Carole Morin and Catherine Deshaies-Moreault for methodological advice and Camélia St-Denis and Darren Wilson (all from Statistics Canada) for their work on the survey and validation of results. The Survey on Vaccination during Pregnancy was conducted by Statistics Canada and funded by the Public Health Agency of Canada.

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