New information from the CDC shows that twenty-six preschoolers in Leon County, Fla, have become sick with pertussis or pertussis-like symptoms.

Officials attributed this outbreak to a combination of the children’s incomplete vaccination status, waning immunity due to vaccine type, possible provider error, and perhaps the emergence of vaccine-resistant bacteria.

The “attack rate” among children age 1-5 at the preschool was 22%, reported James Matthias, MPH, of the Florida Department of Health in Tallahassee, and colleagues writing in Emerging Infectious Diseases.

Another 13 cases were identified among staff members at the preschool, household contacts of the sick preschoolers, and camp counselors who came into contact with a sibling of an ill child.

Among the 33 children (including household contacts) who developed pertussis, 28 had received at least three pertussis vaccinations and 23 had received four or more. Matthias and colleagues estimated the vaccine effectiveness at 45.0%, though with an extremely broad 95% confidence interval (-70.4% to 82.2%).

Of the 39 total cases, 11 had a diagnosis of pertussis confirmed by laboratory testing or epidemiologically linked household contacts, and 28 were identified as “probable.” Out of 117 total children, five were incompletely vaccinated, and two of those developed pertussis.

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