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Are Whooping Cough Shots Effective Enough?

Photograph by Twenty20

A whooping cough outbreak in a Florida preschool three years ago may be a sign that the benefits of this childhood vaccine wanes earlier than previously thought. Over 5 months (starting in September 2013), more than 33 children and two adults, who were either staff members and students (or family members of either) at a preschool in Leon county came down with pertussis, known commonly as whooping cough.

A study of the pertussis outbreak was published recently in the journal Emerging Infectious Diseases, after Florida epidemiologists noted that among the school's students, there was a relatively high rate of on-schedule and up-to-date vaccines: only five of the 117 preschoolers were not up to date. This is the first U.S. outbreak among such a highly vaccinated group of toddlers and preschoolers, researchers wrote in the journal. That age group is thought to be well-protected against whooping cough through vaccines.

The doctors were well aware that people can still come down with pertussis, even after vaccination. Usually, though, it's a milder form of the highly contagious bacterial infection. What was unusual in the Florida case is how long the outbreak lasted in a community with such high rates of immunization.

So they looked a little deeper. What they found was that of the 33 kids in the outbreak, 28 had gotten at least three or more pertussis shots; of those, 23 had actually had four or more. It was the 3-year-olds who had the highest rate for whooping cough during the outbreak. This led the epidemiologists to wonder whether the effectiveness of the shot was wearing out sooner than medical officials thought. The recommended schedule for pertussis shots is a series of five given to children at 2, 4 and 6 months, and then between 15 and 18 months. Another dose is recommended between age 4 and 6, with a booster between 11 and 18 years old.

They also figured out that those who had come down with pertussis weren't properly treated, leaving others exposed to the highly contagious disease. Apparently, doctors weren't testing for the disease, despite news of the local outbreak.

The doctors writing the report are recommending further monitoring of pertussis outbreaks in order to decide whether tweaking of the schedule or more studies of the shot itself are in order.

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