Maternal pertussis vaccinations, given during pregnancy, prevent an estimated 65% of pertussis infections in infants, new research indicates.
The study, led by Annette K. Regan, PhD, MPH, a perinatal and pediatric infectious disease epidemiologist at Curtin University, Perth, Australia, was published online in Pediatrics.
Dr. Regan – who is also with the University of San Francisco and the University of California, Los Angeles – and colleagues reviewed data on 279,418 infants born to 252,444 mothers in Australia.
There, about 52% of the women in this study received the Tdap vaccine through a maternal pertussis vaccination program.
Duration of effectiveness in infants was one of the main questions the study sought to answer.
The authors wrote that they assessed vaccine effectiveness through 18 months of age. “We observed significant protection against disease until at least 8 months of age, 2 months longer than reported in previous studies.” From 70% to 90% of all pertussis-attributable hospitalizations and death occur in infancy.
Answering the ‘blunting’ question
This study also set out to clarify an important clinical question regarding a potential “blunting” effect in infants. Previous work had suggested that maternal antibodies from the vaccination could interfere with the effectiveness of infants’ DtaP (the version of Tdap for infants) and other vaccines.
Dr. Regan and colleagues found that, “although we observed slightly lower VE [vaccine effectiveness] point estimates for the third dose of infant pertussis vaccine among maternally vaccinated compared with unvaccinated infants (76.5% vs. 92.9%, P = .002), we did not observe higher rates of pertussis infection (hazard ratio, 0.70; 95% confidence interval, 0.61-3.39).
Best time to give mothers the vaccine
Another clinical debate has centered on when to give the mother the vaccine during pregnancy. The authors concluded: “Our findings support the infant health benefits of recommendations to administer a booster dose of pertussis vaccine near 28 weeks of gestational age.”
That 28-week mark was associated with lower risk of infection in infants through 8 months of age, they wrote.
Positive results in the United States
In an invited commentary, Kathryn M. Edwards, MD, with the division of infectious diseases, department of pediatrics, at Vanderbilt University Medical Center, Nashville, Tenn., highlighted similar positive findings for maternal pertussis vaccination in the United States.
The Centers for Disease Control and Prevention did an ecologic study of infant pertussis cases reported between Jan. 1, 2000, and Dec. 31, 2019. Rates were compared for the years before maternal Tdap vaccinations were recommended against the 7-year period after they were implemented.
That study found that in the period before maternal Tdap vaccination, annual pertussis incidence did not change among infants younger than 2 months and increased slightly in infants 6-12 months.
However, during the period after maternal Tdap vaccination had started (2012-2019), pertussis incidence significantly decreased in infants younger than 2 months and was unchanged in infants 6-12 months.
“As with the Australian data, the U.S. data support the overall benefit of the maternal Tdap program and, as with the Australian data, do not suggest that blunting has led to an increase in cases within the first year of life,” Dr. Edwards wrote.
The CDC notes that pertussis cases are rising and outbreaks are happening across the United States.
“On average, about 1,000 infants are hospitalized and typically between 5 and 15 infants die each year in the United States due to pertussis,” the CDC states.