Most Pertussis Cases in Infants Tied to Unvaccinated Mother

Laurie Barclay, MD

October 01, 2018

Overall, only 30% of pregnant women whose infants developed pertussis were appropriately vaccinated with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap), according to a study published September 28 in the Morbidity and Mortality Weekly Report. Barriers to vaccination were attending a prenatal clinic that did not stock Tdap vaccine and having Medicaid rather than private insurance, regardless of whether the clinic stocked Tdap.

"[S]tocking vaccines on-site in prenatal clinics is the best way to ensure that all pregnant women are vaccinated and reduce the incidence of pertussis among infants too young to be vaccinated," write Sarah New, MPH, from the Immunization Branch, California Department of Public Health, and colleagues.

In the current study, California local health department personnel identified mothers of all 114 infants younger than 4 months known to have pertussis onset during 2016. Of these mothers, 66 (58%) were interviewed, and their prenatal care providers completed a supplemental questionnaire.

Among the 26 (39%) women who received Tdap during pregnancy, 24 (92%) were vaccinated at their provider's office, and most (80%) were vaccinated according to Advisory Committee on Immunization Practices recommendations, during 27 to 36 weeks' gestation (median, 32 weeks).

Vaccination appeared to reduce both the likelihood of disease and the severity of disease. Among the 40 interviewed mothers (61%) not vaccinated with Tdap during pregnancy, 20 (50%) of their infants were hospitalized, including eight admitted to an intensive care unit and one who died.

In contrast, among the 20 infants whose mothers were vaccinated between 27 and 36 weeks' gestation, four were hospitalized, but none needed intensive care unit admission. Among the five infants whose mothers received Tdap at other times, two were hospitalized, including one who was admitted to the intensive care unit admission and subsequently died.

Mothers whose providers stocked Tdap vaccine on-site were three times more likely to have been vaccinated (relative risk, 3.3; 95% confidence interval, 1.9 - 5.5), compared with women whose providers did not stock the vaccine.

Compared with mothers with private insurance, those with Medicaid were significantly less likely to receive prenatal Tdap (relative risk, 0.4; 95% confidence interval, 0.2 - 0.8), or to receive it during 27 to 36 weeks' gestation, even when it was stocked on-site (relative risk, 0.5; 95% confidence interval, 0.3 - 1.1).

The authors interviewed 61 prenatal care providers regarding their Tdap vaccine stocking policies. Of those, 34 (56%) stocked Tdap vaccine on-site. The most common reasons given for not stocking Tdap were cost (44%) and reimbursement (41%) issues.

The authors recommend incorporating Tdap vaccination into routine prenatal care visits as an effective means to increase coverage.

Advisory Committee on Immunization Practices Recommends Timely Tdap Administration

The Advisory Committee on Immunization Practices recommends vaccinating pregnant women with Tdap as early as possible between 27 and 36 weeks' gestation during every pregnancy as the best way to protect young infants against whooping cough. Most severe and fatal cases occur in infants who have not begun the primary pertussis vaccination series.

However, prenatal Tdap vaccine coverage in California remains low (52% overall; 40% among women with Medicaid).

"A recommendation by prenatal care providers for their pregnant patients to receive Tdap is important, particularly among providers who do not stock Tdap vaccine on-site," the study authors write. "[I]t is important to provide pregnant patients with specific information about where they can receive Tdap vaccination and to follow up at subsequent visits to ensure Tdap vaccine is received within the recommended time frame."

Referral for Tdap vaccination should be to an accessible site covered by the mother's insurance. Approximately 40% of the unvaccinated mothers in this analysis never received any recommendation or referral for Tdap vaccine, or were not vaccinated for reasons not cited by current Advisory Committee on Immunization Practices recommendations, and 20% refused prenatal Tdap. Postpartum vaccination with Tdap occurred in 40% of the mothers unvaccinated during pregnancy, which has not been recommended since 2011, highlighting the need for provider education about current recommendations.

"Promoting on-site prenatal vaccination, educating providers about Tdap recommendations, and strengthening off-site referral likely will improve Tdap vaccination coverage during pregnancy," the study authors note.

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. 2018;67(38);1068-1071. Full text

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