Bordetella pertussis and Pertussis Disease
Overview of Bordetella pertussis
Bordetella pertussis is a bacterium responsible for causing pertussis, also known as whooping cough, which can be particularly severe in infants. The incidence of pertussis has risen over the years, with 20,762 confirmed cases reported in 2015.
Impact on Infants
Infants are significantly affected by pertussis, with at least half of all related deaths occurring in this age group. This high mortality rate has led the Centers for Disease Control and Prevention (CDC) to recommend the diphtheria, tetanus, and acellular pertussis (DTaP) vaccine for infants at two, four, and six months, along with booster shots at 15-18 months and 4-6 years.
Recommendations for Pregnant Women
The CDC also advises administering the Tdap booster vaccine to pregnant women. Since vaccinations are scheduled, children are considered fully protected only after receiving the third dose of the DTaP vaccine by six months of age. However, the Tdap booster has not significantly reduced pertussis incidence in infants. Consequently, the CDC suggests that the Tdap booster for pregnant women can help provide immunity to their unborn child through the placenta.
Debate on Optimal Timing for Booster Administration
Research on Booster Timing
Ongoing research has raised questions about the best timing for administering the Tdap booster to maximize protection for infants. Current CDC guidelines recommend giving the booster during the third trimester, but researchers are still debating whether administration in the second or third trimester is more effective.
Study on Tdap Effectiveness
A study conducted by Becker-Dreps and colleagues, published in the American Journal of Preventive Medicine, sought to evaluate the effectiveness of the Tdap vaccine at different gestational stages. The research analyzed data from 1,079,034 pregnant women between 2010 and 2014. Participants were categorized based on when they received the Tdap vaccine: either more than two weeks before delivery (prenatal Tdap) or less than two weeks, including the day of delivery or within seven days postpartum (postpartum Tdap).
Findings on Tdap Vaccine Effectiveness
Impact on Infant Pertussis Rates
The study found that infants whose mothers received the prenatal Tdap vaccination experienced a 43% reduction in pertussis rates. Additionally, inpatient-only cases of pertussis were 68% lower in this group compared to infants of unvaccinated mothers. Notably, if mothers were vaccinated at or after 27 weeks of gestation, their infants had a lower likelihood of developing pertussis compared to those whose mothers were vaccinated before 27 weeks.
Postpartum Vaccination Outcomes
Infants of mothers who received the Tdap vaccine postpartum also showed reduced rates of pertussis compared to those whose mothers did not receive the vaccine. The overall effectiveness of the Tdap vaccine against pertussis in infants varied according to the age of the children.
Conclusion and Limitations of the Study
Overall Effectiveness of Third-Trimester Vaccination
The study concluded that administering the Tdap vaccine during the third trimester resulted in fewer cases of pertussis in infants compared to mothers who were unvaccinated. However, there was no statistical evidence supporting benefits from vaccination before the third trimester or during the postpartum period.
Study Limitations
Several limitations were identified in the study, including potential misclassifications of pertussis cases based on symptoms rather than laboratory confirmation. Technical errors, such as misalignment of mothers and their infants, may also have occurred. Furthermore, early immunization estimates were less precise than those for the post-27-week group, which had a larger sample size. Additionally, since the study focused on insured populations, results may not accurately reflect outcomes in uninsured individuals.
Reference
Becker-Dreps, S et al. Effectiveness of Prenatal Tetanus, Diphtheria, Acellular Pertussis Vaccination in the Prevention of Infant Pertussis in the U.S. Am J Prev Med. (2018). doi: 10.1016/j.amepre.2018.04.013.