False-color transmission electron micrograph of a field of whooping cough bacteria, Bordetella pertussis. A. Barry Dowsett/Science Source hide caption

itoggle caption A. Barry Dowsett/Science Source

A student gets vaccinated against pertussis at a Los Angeles middle school in 2012. The state required that students be immunized to halt an epidemic of whooping cough. Kevork Djansezian/Getty Images hide caption

itoggle caption Kevork Djansezian/Getty Images

At a Los Angeles media briefing in 2010, Mariah Bianchi describes how her own case of whooping cough caused the death of her newborn son. Reed Saxon/AP hide caption

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Nurse Fatima Guillen (left) gives 4-year-old Kimberly Magdeleno a whooping cough booster shot at a health clinic in Tacoma, Wash., in May. Ted S. Warren/AP hide caption

itoggle caption Ted S. Warren/AP

Pharmacist Kristy Hennessee administers a vaccination against whooping cough in Pasadena, Calif., in 2010. Vaccinations are the most powerful weapon for slowing the epidemic, but there are growing concerns that the current vaccine doesn't last as long as expected. Robyn Beck/AFP/Getty Images hide caption

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A nurse in Washington administers the whooping cough vaccine to a child in May. In response to the epidemic, more than 82,000 adults have also received the vaccine this year. Ted S. Warren/AP hide caption

itoggle caption Ted S. Warren/AP

Nurse Susan Peel gives a whooping cough vaccination to a high school student in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness by the time people reach their teens and early adulthood. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP

Nurse Susan Peel gives a whooping cough vaccination to a student at Inderkum High School in Sacramento, Calif., in 2011. Now it seems likely such shots will become routine for senior citizens, too. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP