Pregnant women should be immunized against whooping cough at each pregnancy to protect their newborns from the disease, the CDC's Advisory Committee for Immunization Practices has recommended.
The Tdap shot against pertussis, tetanus, and diphtheria should be given in the third or late second trimester, the committee agreed by a 14-0 vote, with one abstention.
If approved, the committee's recommendation would replace the 2011 guidance urging that pregnant women get the shot during pregnancy or immediately postpartum if they had not been previously vaccinated.
The proposed change comes in the context of an outbreak of pertussis that the committee was told has caused 32,645 cases in the U.S. as of Oct. 12, as well as 16 deaths.
Most of the deaths were "in the first few months of life, an age where we cannot protect the infant directly," noted Mark Sawyer, MD, of the University of California San Diego, who is chair of the committee's pertussis working group.
The vaccine that protects against pertussis in young children -- the diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP) -- is administered in five doses at 2, 4, 6, and 15 to 18 months, with a final dose around 4 to 6 years old, but before the child starts school.
But in the early months of the vaccination schedule, the child is not fully protected, leading to efforts to find indirect protection by immunizing the mother, as well as others who will be in contact with the baby.
(The vaccine names are similar, but they have different doses of the various components.)
The current outbreak, the committee was told, seems likely to become the largest since 1959 when all the numbers are in.
Overall, the incidence rate is 10.6 cases per 100,000 population, but that varies widely by state -- 32 states have at least twice the number of cases so far this year than they had last year, the committee was told.
The committee was told that giving Tdap during pregnancy seems to be "acceptably safe" and leads to higher levels of pertussis antibodies in the newborn.
Despite that, only 2.6% of women are vaccinated during their pregnancy.
In the original discussion of immunization during pregnancy, in 2011, the committee was told that a mathematical model found important reductions in infant pertussis incidence, hospital admissions, and mortality, according to Jennifer Liang, DVM, of the CDC, a member of the pertussis working group.
Giving women a shot during pregnancy led to a 33% reduction in cases, a 38% drop in hospital admissions, and a 49% drop in deaths, compared with the "base case" in which no vaccinations were given, Liang said.
Postpartum immunization also had an effect, she said, but it was not as great as vaccinations during pregnancy.
But immediately after the 2011 recommendation, questions arose about what should happen during subsequent pregnancies for women already immunized once, Liang said, especially since there is evidence that Tdap immunity wanes over time.
Liang said there is evidence that maternal antibodies are effectively transferred to the infant, but not if the immunization comes before conception – at a previous pregnancy, for example – or early in gestation.
But, she noted, the Tdap vaccines now on the market are licensed for a single adult use, so there is some question about the safety of multiple doses.
But analysis of available data suggested that even short intervals between vaccinations do not lead to increased rates of serious adverse events, she said, with most adverse events being such things as injection site pain and redness.
Birth statistics suggest that most U.S. women have only two babies and the deliveries are usually separated by 13 months or more, Liang said. The numbers are "reassuring" that only a small proportion of women would get more than two or three doses of the vaccine, she said.
At the same meeting, ACIP members voted 13 to 1, with 1 abstention to recommend that infants at increased risk for meningococcal disease be vaccinated with HibMenCY at 2, 4, and 6 months and again between 12 and 15 months of age.
Recommendations from ACIP do not become final until accepted by the director of the CDC and published in Morbidity and Mortality Weekly Report. All ACIP recommendations have been accepted in the past.