Whooping Cough Rates Raise Questions About Vaccine

The rising rate of whooping cough cases in the United States may signal the reduced efficacy of the acellular pertussis vaccine, according to a new report.

Researchers at the US Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) reported a gradual and sustained increase in pertussis since historic lows in the 1970s, with the last peak year being 2010, with 27,000 reported cases and 27 deaths, 25 of them infants. Since mid-2011, a substantial rise in pertussis cases has been reported in the state of Washington, with the reported number of cases by June 2012 reaching 2,520, a 1,300% increase compared with the same period in 2011, and the highest number of cases reported in any year since 1942.

These figures are consistent with national trends, with high rates of pertussis observed among infants aged younger than one year and children aged 10 years. However, the incidence in adolescents aged 13-14 years also was increased, despite high rates of vaccination with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine. According to the researchers, the increase in pertussis among these, who received only the acellular pertussis vaccine, and not the whole-cell version, suggests a waning of the vaccine. The report was published in the July 20, 2012, issue of Morbidity & Mortality Weekly Report.

“The highest rates are in infants under a year old, with half of cases occurring in infants younger than 3 months who couldn't yet be vaccinated; nine infant deaths have been reported,” said Anne Schuchat, MD, director of the National Center for Immunization and Respiratory Diseases at the CDC. “Their immunity depends on that of the people around them. All pregnant women and other people who are going to come in contact with infants -- grandparents and healthcare professionals, for instance -- should receive the Tdap booster.”

The switch from whole-cell pertussis to acellular pertussis was made in 1997, due to concerns over a possible (though unproven) link to chronic neurologic problems, as well as more severe injection-site reactions and fever. Today, children receive a five-dose series of the DTaP vaccination beginning at age 2 months, followed by a booster Tdap shot at age 11 or 12.

Related Links:
US Centers for Disease Control and Prevention