The decision from the US Food and Drug Administration (FDA), announced on Friday, approves Boostrix (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine adsorbed [Tdap]) for immunisation during the third trimester of pregnancy to help prevent pertussis (whooping cough) in infants less than two months of age.
The FDA’s approval of Boostrix already included its use during pregnancy to protect the mother. However, the new approval is specific to use in pregnancy to prevent pertussis in newborn infants under two months old.
The vaccine was first approved in 2005 for use in adolescents aged 10-18 years against tetanus, diphtheria and whooping cough.
Most serious whooping cough cases are in youngest infants
The US sees frequent outbreaks of whooping cough; with the most serious cases – including hospitalizations and deaths – occurring in infants younger than two months old who are too young to be protected by the childhood pertussis vaccine series.
According to the Centers for Disease Control and Prevention (CDC), 4.2% of the total cases of the respiratory disease reported in the US in 2021 were in infants younger than 6 months of age and approximately 31% required hospitalization.
When the Boostrix vaccine is given during pregnancy, it boosts antibodies in the mother, which are transferred to the developing baby.
The effectiveness of Boostrix administered in the third trimester on young infants was based on a re-analysis of the Boostrix-relevant data from an observational case-control study of Tdap vaccine effectiveness.
In this re-analysis, data from 108 cases of pertussis in infants younger than 2 months of age (including four cases whose mothers received Boostrix during the third trimester) and 183 control infants who did not have pertussis (including 18 whose mothers received Boostrix during the third trimester) resulted in a preliminary estimate of Boostrix as 78% effective in preventing pertussis among infants younger than 2 months of age, when administered during the third trimester of pregnancy.
The safety of Boostrix administered during the third trimester of pregnancy was assessed in a randomized, placebo-controlled study with a non-U.S. formulation of Boostrix (The FDA deemed the formulation relevant because it contains the same components as the US formulation, with the exception that the non-US formulation contains more aluminum per dose).
This study included approximately 680 pregnant individuals of whom about 340 received Boostrix and of whom about 340 received saline placebo. After childbirth, the placebo recipients were then vaccinated. The rates of reported side effects following receipt of Boostrix administered during pregnancy were consistent with the rates following receipt of Boostrix administered to study participants after childbirth.
The study did not identify any vaccine-related adverse effects on pregnancy or on the fetus or newborns.
“Pertussis disease is a highly contagious respiratory illness affecting all age groups. However, babies are at highest risk for getting pertussis and having serious complications from it,” said Peter Marks, M.D., Ph.D., director of the FDACenter for Biologics Evaluation and Research. “While vaccination is the best method for providing protection, infants younger than two months of age are too young to be protected by the childhood pertussis vaccine series. This is the first vaccine approved specifically for use during pregnancy to prevent a disease in young infants whose mothers are vaccinated during pregnancy.”