Study finds herd immunity protects babies against whooping cough

While doubts about the effectiveness of whooping cough vaccines from GlaxoSmithKline ($GSK) and Sanofi ($SNY) have mounted over the past year, health authorities have stressed that the vaccines are helping. These voices gained supporting data this week when researchers found evidence of herd immunity effects.

Babies receive their first whooping cough vaccine at two months of age and need another four shots over the next 7 years. This gradual building of immunity is intended to protect newborns from serious side effects, which become less likely as the child ages, but creates a window in which infants are vulnerable to whooping cough. Writing in Pediatrics, researchers report that immunizing adolescents against whooping cough, also known as pertussis, appears to be reducing hospitalizations of infants.

In 2008, 2009 and 2011 the observed rate of hospitalizations of infants aged one year and under was significantly lower than expected. The disparity was most pronounced in 2011. Without Tdap--the combo vaccine that protects against pertussis--researchers estimated there would have been 10.7 hospital visits per 10,000 infants. In reality there were 3.3. "Now we have data that it works, we have created another reinforcing reason to bring teens in for vaccination, not only against whooping cough but for other diseases as well," Vanderbilt University's Dr. William Schaffner told CNN.

Researchers think the data show that vaccination of adolescents is cutting the number who pass the bacterial infection on to their younger, unprotected siblings. Previous studies have found that older siblings are the source of the infection for half of infants who contract whooping cough. "[The vaccine] helps adolescents, but in turn, it indirectly protects babies even more. [It's a] win-win situation and I don't see any major downsides," pediatrician Dr. Jennifer Shu said.

- here's the CNN post
- check out the Pediatrics abstract

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