BACKGROUND: Pertussis is a vaccine-preventable illness that can cause severe disease, even death, in infants. Infants are especially vulnerable because they cannot be vaccinated against pertussis before six weeks of age. In 2013, the CDC recommended that pregnant women receive a pertussis vaccine (Tdap) every pregnancy to protect the mother and to pass immunity in utero to the child. Texas began collecting maternal vaccination status for pertussis cases in late 2013.
METHODS: Pertussis cases in Texas were classified according to the CSTE 2014 case definition. Proxies for reported cases were interviewed using a standard investigation form and responses entered into a central database. Data analysis was performed using Excel. Age at date of cough onset was calculated. Mother’s vaccination status during pregnancy was self-reported. Maternal vaccination received within one week of the child’s birth was categorized as received at delivery. Infant was defined as a child that had not yet turned one at the time of cough onset.
RESULTS: As of 12/31/15, 282 infant pertussis cases were reported for 2015, which is 20.0% of all cases in Texas. Of the infant cases, 77 (27.3%) required hospitalization. Maternal vaccination status for infant cases broke down as follows: not vaccinated 39.4%, unknown 30.9%, vaccinated at delivery 18.1%, and vaccinated prenatally 11.7%. Overall 84 infants (29.8%) were born to mothers that received pregnancy-associated Tdap. The relative risk (RR) of infants with pertussis being hospitalized if the mother was not vaccinated was 1.4 (95% confidence interval [CI]: 0.9, 2.5) times that of the infants whose mothers were vaccinated at delivery. The hospitalization RR for infants whose mothers were not vaccinated was 4.0 (95% CI: 1.3, 12.3) times that of infants whose mothers did receive prenatal Tdap.
CONCLUSIONS: Vaccinating pregnant women against pertussis appears to mitigate hospitalization risk in the event their babies become infected with pertussis in the first year of life. Reduction of hospitalization risk among infants whose mothers were vaccinated at time of delivery is not statistically significant. The percent of mothers who were unvaccinated was 39%, indicating a need for better outreach to providers and pregnant women. Outreach messaging should focus on vaccination during pregnancy, not at delivery. This study is limited by use of self-reported data and missing data. Better collection of maternal vaccination status is needed. To that end, Texas plans to improve capture of this information through refining interview questions and techniques and finding secondary sources of data (e.g. immunization registries).