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The Person Most Likely to Infect Your Baby With Pertussis Is...

Think you're covering all of your bases by making sure Grandma is up to date on her vaccinations before visiting your newborn? Think again.

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Think you're covering all of your bases by making sure Grandma is up to date on her vaccinations before visiting your newborn? Think again.

According to a new study published Monday in Pediatrics, it's older siblings who are most likely to spread the whooping cough bacteria to your babe—even if they're already vaccinated. That's because evidence suggests there's a waning immunity among children and tweens who received their diphtheria and pertussis shots.

In the study, researchers analyzed data from 1,306 cases of infant pertussis reported between 2006 and 2013. Not surprisingly, in two-thirds of the cases, the infection came from members of the baby's immediate family. More specifically, dads were the source of 10 percent of the cases, moms of 20.6 percent, and siblings of 35.5 percent.

These stats fly in the face of the previously held belief that mamas were the most common source of infection of pertussis in babies.

That doesn't mean moms are entirely off the hook. Though "infant cocooning," or making sure visitors are vaccinated before holding a newborn, has its share of benefits (and supporters), a mother's safest bet is to get the Tdap vaccination, or tetanus-diphtheria-pertussis vaccination, during pregnancy. This simple prenatal precaution remains the most effective way to protect very young babies against this highly contagious disease, and skipping it could have very serious consequences. According to the Centers for Disease Control and Prevention, whopping cough was responsible for 277 deaths between 2000 and 2014. The victims in nearly every case? Babies younger than 3 months, who were too young to receive vaccinations.

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Bonnie Gibbs Vengrow is a New York City-based writer and editor who traded in her Blackberry and Metro card for playdates and PB&J sandwiches—and the once-in-a-lifetime chance to watch her feisty, funny son grow up. Follow her on TwitterPinterest, and Google+.

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