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

Abstract

Background: Infants aged <1 year are at highest risk for pertussis-related morbidity and mortality. In 2012, Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) vaccine was recommended for women during each pregnancy to protect infants in the first months of life; data on effectiveness of this strategy are currently limited.

Methods: We conducted a case-control evaluation among pertussis cases <2 months old with cough onset between 1 January 2011 and 31 December 2014 from 6 US Emerging Infection Program Network states. Controls were hospital-matched and selected by birth certificate. Mothers were interviewed to collect information on demographics, household characteristics, and healthcare providers. Provider-verified immunization history was obtained on mothers and infants. Mothers were considered vaccinated during pregnancy if Tdap was received ≥14 days before delivery; trimester was calculated using Tdap date, infant's date of birth, and gestational age. Odds ratios were calculated using multivariable conditional logistic regression; vaccine effectiveness (VE) was estimated as (1 - odds ratio) × 100%.

Results: A total of 240 cases and 535 controls were included; 17 (7.1%) case mothers and 90 (16.8%) control mothers received Tdap during the third trimester of pregnancy. The multivariable VE estimate for Tdap administered during the third trimester of pregnancy was 77.7% (95% confidence interval [CI], 48.3%-90.4%); VE increased to 90.5% (95% CI, 65.2%-97.4%) against hospitalized cases.

Conclusions: Vaccination during pregnancy is an effective way to protect infants during the early months of life. With a continuing resurgence in pertussis, efforts should focus on maximizing Tdap uptake among pregnant women.

Keywords: Tdap; infant; maternal immunization; pertussis.

Figure 1a. Timing of Tdap Doses Classified as During Pregnancy

The white bars represent Tdap doses received by control-associated mothers during pregnancy, and the gray bars represent Tdap doses received by case-associated mothers during pregnancy. *2 cases were missing gestational age so the exact week of Tdap administration could not be calculated; based on date of birth and Tdap date, both cases were included in the second trimester of pregnancy in the analysis models.

Figure 1b. Timing of Tdap Doses Classified as Before Pregnancy

The white bars represent Tdap doses received by control-associated mothers before pregnancy, and the gray bars represent Tdap doses received by case-associated mothers before pregnancy. *1 case missing gestational age so the exact month of Tdap administration before pregnancy could not be calculated; based on date of birth and Tdap date, this case was included in the ≤2 year group in the analysis models.

Figure 1c. Timing of Tdap Doses Classified as Post-partum

The white bars represent Tdap doses received by control-associated mothers during the post-partum period, and the gray bars represent Tdap doses received by case-associated mothers during the post-partum period.