The sharp rise in U.S. pertussis cases in recent years may be attributable to increases in nonmedical vaccine exemptions for children and waning immunity, according to a new study published in PNAS.
While the incidence of pertussis — commonly referred to as whooping cough — experienced a significant decline after the vaccine for the bacterial illness launched in the 1940s, pertussis rates increased marginally in the 1980s and 1990s, then jumped in the mid-2000s. In 2012, the U.S. saw 48,000 cases of pertussis, the largest number on record since 1955.
To assess the potential influence of nonmedical vaccine exemptions on pertussis rates, researchers analyzed county-level data on pertussis and vaccine exemptions for Arizona, New Jersey, Oregon, Utah and Washington. Each of the five states had pertussis incidence rates above the national baseline in 2012. Forty-five percent of the counties had high rates of nonmedical vaccine exemptions. Researchers also examined clusters of pertussis outbreaks among two different age groups: children aged 5 years and younger and children aged 10 to 14 years.
"Our paper shows two things. One is that when you look at counties that have a lot of pertussis cases, they are the same counties that also have a high level of vaccine exemptions, which suggests an association between the two," said Barry Bloom, PhD, Joan L. and Julius H. Jacobson Research Professor of Public Health at Harvard Chan School of Public Health in Boston. "Our other finding is that 10- to 14-year-olds who had been vaccinated were as susceptible to pertussis as kids who had never been vaccinated — suggesting that the vaccine's effectiveness was not long lasting."
Pertussis is characterized by uncontrollable, violent coughing, which can persist for weeks or months. The bacteria are spread from hand-to-hand contact, sneezing or coughing. Infants, young children and the elderly are at the highest risk for complications. For babies less than a year old, the illness can be deadly.
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