Preparedness, prevention, and pertussis

July 9th, 2010 by CHHS RAs

By Melissa Kim
CHHS Research Assistant, summer 2010

After 910 confirmed cases and the deaths of five infants, California declared an epidemic of whooping cough, also known as pertussis, on June 23.  With 600 more possible cases under investigation and the expected peak still to come in July or August, this could be the state’s worst pertussis outbreak in 50 years.  California is not alone in this crisis.  Outbreaks have also been reported in Illinois, Michigan, and Oregon, with increased numbers of cases across the country.

Pertussis outbreaks are cyclical and recur every 2-5 years.  The last episode in California was in 2005, with 3,182 cases and eight deaths.  Logic would beg the question: “If pertussis is a disease we can expect to see every few years and we have a vaccine to stop it, why are the numbers of cases increasing and not decreasing?”

Several potential factors contribute to the increase in pertussis cases.  Probably the most striking of these is the controversial anti-vaccine movement driven by the fear of a possible link between vaccines and autism. Although the article claiming the link was retracted by the journal that originally published it, and the article’s author was discredited and even stripped of his medical license, the damage was already done.  Parents concerned with vaccine safety are filing “personal belief exemptions” (PBE) that waive the requirement for childhood vaccinations prior to attending school.  This vaccine-phobia has increased PBE rates to as high as 70% in some schools, leaving only 30% of the students with proper protection.  As expected, a 2009 study in Pediatrics found that children of parents who refuse the pertussis vaccination are at significantly higher risk for infection when compared to vaccinated children.

Another factor contributing to the outbreaks is the misconception that vaccination or previous illness from pertussis provides lifelong immunity.  In fact, the pertussis vaccine (DTaP) only provides 5-10 years of protection, after which an additional booster shot (Tdap) is recommended for adolescents and adults.  Currently, only 41% of the nation’s adolescents have coverage for whooping cough. For adults, that number is an alarming 6%.

Language barriers and a lack of immunizations in rural areas may also be contributing to the outbreaks.  This is suspected to be the case in Fresno County, which is home to many Latino farm workers and has the highest number of cases in California, with 72 cases in May alone.

Regardless of the reason behind the recent pertussis outbreaks, some experts say the most effective way to break this escalating trend and prevent future outbreaks is to vaccinate everyone, especially family members of new infants, before they leave the hospital.  Because newborns are too young to receive vaccinations, their protection from pertussis depends on herd immunity, where the vaccinated protection of the masses prevents disease transfer to the unvaccinated few.  In order to effectively shield this vulnerable population, studies show that vaccination rates need to increase to at least 93%. When you consider parents refusing to vaccinate their children, the high rates of adolescents and adults missing their booster shots, and the many barriers to healthcare access, 93% is a daunting goal.

These challenges highlight the need for a concerted public health education effort in the United States to promote the life-saving benefits of getting vaccinated for whooping cough and other contagious but preventable diseases. The Centers for Disease Control and Prevention is already making headway, offering educational materials in several languages to help state and local health departments implement vaccination recommendations for specific age groups. It’s a start, but we still have a long way to go.

More information on pertussis outbreaks reported in Illinois, Michigan, and Oregon can be found at the links below:


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