This week, GSK announced in a press release that the US Food and Drug Administration (FDA) had approved Boostrix as an immunization for pregnant women for the prevention of whooping cough in newborn infants. Boostrix is the first vaccine in the US indicated for the protection of newborns under two months of age from pertussis. The vaccine is a Tdap vaccine (Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular Pertussis Vaccine, Adsorbed) that can be administered during the third trimester of pregnancy.
Whooping cough, also known as pertussis, is a highly contagious respiratory infection caused by the Bordetella pertussis bacteria. Its name comes from the resultant hacking cough, followed by a sharp, high-pitched gasp that sounds like a “whoop”.
Prior to the development of vaccinations for the condition, whooping cough was thought to be a childhood disease. Presently, it mostly affects children too young to have received the full course of vaccinations, as well as adults whose immunity has worn off.
Although deaths are rare, they occur most commonly among infants younger than two months of age as they are still too young to receive protection from the childhood pertussis vaccines.
The Centers for Disease Control and Prevention (CDC) reported that in 2021, 4.2 percent of pertussis cases in the US were in infants under six months of age, and 31 percent of those cases required hospitalization. Since infant immune systems are still developing, they are more susceptible to complications. Thus, it is important for pregnant individuals and close contacts of the infant to be vaccinated against pertussis.
Initially, Boostrix was approved by the FDA in 2005 as a single booster Tdap vaccine for individuals aged 10 to 18. The FDA then approved its use in individuals over 19 years of age as an additional dose nine or more years after the initial Tdap vaccine.
The approval highlighted in the press release is specific for use during pregnancy to prevent pertussis in newborns under two months of age, even though it has been recommended by the CDC since 2012 to use Tdap vaccines in the third trimester of pregnancy.
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Boostrix Effectively Protects Newborns Against Pertussis
When Boostrix is administered during pregnancy, protective antibodies are boosted in the mother and are then transferred to the developing baby.
The efficacy of Boostrix as a vaccine administered during the third trimester was determined based on the re-analysis of existing real-world data from observational case-control study of Tdap vaccine effectiveness. The evidence provided was sufficient to grant approval status. The results included data from 108 pertussis cases in infants under two months of age (including four cases whose mothers received Boostrix during the third trimester) and 183 control infant subjects who did not have pertussis (including 18 cases in which the mothers received Boostrix during the third trimester). A preliminary estimate of 78 percent effectiveness in preventing pertussis in infants was updated using data from the published observational studies, and statistical analyses were consistent with the preliminary estimate.
A separate randomized, placebo-controlled study was conducted to investigate the safety of Boostrix when administered during the third trimester. The study was conducted using a non-US formulation of Boostrix, but the FDA considers the safety data and results relevant because the components are the same in both Boostrix formulations, the non-US option only contains more aluminum per dose. There was an even split of 680 pregnant individuals into the treatment and saline placebo arms. The individuals who received the placebo were vaccinated with the non-US Boostrix formulation after childbirth. The rates of reported side effects after administration during pregnancy were consistent with those reported by participants who received the vaccine after childbirth.
No adverse events related to the vaccine were reported in the study for the mother, fetus, or newborn. Additionally, the side effects reported for Boostrix are consistent with those experienced with other vaccines, such as pain and redness at the injection site, headaches and fatigue, and gastrointestinal symptoms.
Boostrix has been approved as a Tdap vaccine in 80 countries, including the US, most of the European Union, Canada, Australia and New Zealand.
Roger Connor, President, Vaccines and Global Health at GSK, stated in the press release that they are “immensely proud to have the first-ever Tdap vaccine approved by the FDA specifically for this use during pregnancy. We believe this approval may help protect more infants from the potentially life-threatening implications of whooping cough.”