Cases of whooping cough, or pertussis, have been increasing in recent years. Public health officials have been looking for the best ways to reduce the disease in young babies.
Pertussis involves extremely intense coughing that can last for many weeks or months, and it can kill babies.
A recent study found that giving mothers the Tdap shot during the second or third trimester of pregnancy may be a very effective method to reduce pertussis in young babies. The Tdap is the teen and adult booster vaccine shot that protects against pertussis, diphtheria and tetanus.
The shot should be given to all pregnant women, regardless of when their most recent booster shot was, according to the researchers.
That strategy may be the most effective and cost-saving. It also may be more likely to reduce deaths since deaths from pertussis usually occur in babies under 3 months old.
The study, led by Andrew Terranella, MD, MPH, of the Epidemic Intelligence Services at the Centers for Disease Control and Prevention, looked at the effectiveness of pregnant women getting the Tdap to protect their newborns from pertussis.
Approximately 63 out of every 100,000 babies under 1 year old get pertussis each year in the US.
The CDC recommends that all babies receive the DTaP shot at 2 months old to protect against pertussis, diphtheria and tetanus.
The DTaP and the Tdap are very similar vaccines that protect against the same diseases, but the DTaP is given to children under 8 years old.
For this study, the researchers used data from 4,131,019 babies in 2009 who were followed for one year.
The authors analyzed three different strategies for protecting babies under 2 months old from whooping cough.
One strategy was having pregnant women get the Tdap vaccine during the second or third trimester of pregnancy to pass along some of the immunity to her newborn after birth.
A second strategy was for the mother to receive the Tdap vaccine after giving birth so that she was less likely to get sick and pass along whooping cough to her child.
The third strategy – referred to as "cocooning" – was for the mother as well as other family members to get the Tdap vaccine to protect a baby from whooping cough.
In the cocooning strategy, vaccinating the primary people around a baby creates a protective "cocoon" around the child to reduce risk of pertussis.
Parents are the ones who pass whooping cough on to their babies in 50 to 55 percent of all infant whooping cough cases.
In 6 to 8 percent of cases, it's the grandparents who pass it along, and in 20 percent of cases, it's the infant's siblings.
The authors created mathematical models to evaluate the effectiveness of each of these strategies based on data and assumptions about the effects of the vaccine.
The researchers estimated that vaccinating mothers after they give birth would avoid approximately 596 cases of pertussis in babies each year. That would represent 20 percent fewer cases than currently occur.
Having pregnant women get the Tdap during pregnancy would avoid approximately 1,012 pertussis cases in babies each year, the researchers estimated. That would reduce the cases by one-third from their current levels.
These reduced pertussis cases would primarily be among babies who were 1 and 2 months old – those at highest risk for whooping cough.
Using the cocooning strategy by vaccinating a baby's mother, father and a grandparent would avoid 987 pertussis cases in babies, also just under a one-third reduction, the researchers estimated.
However, cocooning would cost more money because of the higher number of vaccinations, and it may be logistically difficult for more people to be vaccinated than just the mothers during pregnancy.
Also, the reduced number of cases that would occur with cocooning tended to be among older age groups than the most at-risk group of babies under 3 months old.
When the researchers analyzed the possible reduction of babies' deaths from pertussis from different strategies, the strategy of vaccinating pregnant women appeared best.
"Pregnancy vaccination reduced infant hospitalizations by 38 percent and deaths by 49 percent relative to base case, compared with reductions of 32 percent and 29 percent for postpartum vaccination with cocooning," the authors wrote.
Overall, therefore, the best strategy to reduce pertussis cases, especially among the youngest babies, appeared to be vaccination of pregnant women during their second or third trimester.
"Our analysis showed that a Tdap dose during pregnancy could avert more infant pertussis cases, hospitalizations, and deaths than postpartum or cocooning strategies," the authors wrote.
This strategy works primarily for two reasons. It offers "earlier indirect protection from vaccinating the mother" so that she is less likely to get sick and pass the disease to her baby.
It also provides some direct immunity to the unborn baby because the mother's antibodies against pertussis can cross the placenta to the growing baby.
Therefore, the CDC recommendation is that all pregnant women get the Tdap shot during their second or third trimester of pregnancy, regardless of when they last had the shot.
The study was published May 27 in the journal Pediatrics.
The research did not use external funding outside of the CDC. The authors declared no conflicts of interest.