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BACKGROUND: Infants <2 months old are at highest risk for severe morbidity and mortality from pertussis because they are too young to be vaccinated. To protect young infants, the Advisory Committee on Immunization Practices (ACIP) recommends vaccination of women with Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine) during every pregnancy. With pertussis still prevalent, high Tdap coverage during pregnancy is key to protecting young infants. We sought to determine maternal Tdap coverage for infant cases and reasons for maternal non-vaccination, and assess for differences in infant pertussis clinical presentation by maternal vaccination status.
METHODS: Cases <1 year old that met the CSTE confirmed or probable case definition were identified through surveillance in seven Enhanced Pertussis Surveillance (EPS)/Emerging Infection Program (EIP) sites between 1/1/2013 and 10/31/2014. Case-patient demographics, clinical symptoms, maternal Tdap (including dates and timing in relation to pregnancy), and reasons for Tdap non-receipt (not mutually-exclusive) were collected during patient and physician interview, or from immunization registries. Case-infants born to mothers vaccinated during pregnancy (VDP) were compared to case-infants born to mothers who received Tdap outside of pregnancy (VOP); Chi-square test was used to compare proportions.
RESULTS: We included 259 pertussis cases <1 year old; 17.8% were <2 months old. One-hundred forty-two (54.8%) mothers had received ≥1 Tdap and 54/142 (38%) of vaccinated case-mothers received Tdap during pregnancy. Of 51 mothers with known timing of vaccination during pregnancy, 94% received Tdap during the 2nd or 3rd trimester. Of the 205 case-mothers not vaccinated during pregnancy, 31.7% reported receiving no recommendation from their physician, 22.0% received Tdap post-partum, 13.2% had another reason, 11.2% received Tdap at some point pre-pregnancy, 5.9% declined vaccination during pregnancy, and 22.0% had unknown reason. The proportion of cases <3 months old was similar between VDPs and VOPs (29.6% vs. 22.7%, p=0.3587). Case-infants born to VOPs were more likely than VDP-born case-infants to have whoop (56.8% vs. 37.0%; p=0.0221) and post-tussive vomiting (72.7% vs. 53.7%; p=0.0206); no differences were observed for apnea, paroxysmal cough or hospitalization status.
CONCLUSIONS: In our analysis, the most common reason case-mothers reported for not being vaccinated during pregnancy was lack of physician recommendation for Tdap during pregnancy. Although some infants get pertussis despite maternal adherence to the pregnancy recommendation, our data suggest that case-infants born to VDPs are less likely than VOP-born infants to present with some of the classic pertussis symptoms, further underscoring the benefits of the strategy.