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Pertussis Outbreaks

Vaccine Preventable Diseases


Updated June 19, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

An 2010 outbreak of pertussis or whooping cough in California caught many people by surprise, after all, most kids get vaccines to protect them against pertussis as infants and toddlers and a booster before they start kindergarten.

There is even a newer tetanus booster shot (Tdap) that includes the pertussis vaccine to help teens and adults get renewed protection against pertussis, which is important, since the immunity that the pertussis vaccine offers is at its strongest for only about 3 years and then gradually decreases over the next 2 to 7 years.

Why So Many Pertussis Outbreaks?

So why is pertussis still a problem? Many teens and adults haven't gotten a Tdap vaccine yet, can still get sick with pertussis, and can infect infants who haven't completed their three dose primary series of pertussis vaccines when they are about six months old. The fact that some parents are refusing vaccines or using alternative immunization schedules likely isn't helping prevent these types of outbreaks of vaccine preventable infections either.

The CDC reports that children who had never received any doses of DTaP (unvaccinated children) faced odds of having whooping cough at least eight times higher than children who received all five doses. And a 2009 study that appeared in Pediatrics reported that "vaccine refusers had a 23-fold increased risk for pertussis when compared with vaccine acceptors, with 11% of pertussis cases in the entire study population were attributed to vaccine refusal." Another article, "Geographic Clustering of Nonmedical Exemptions to School Immunization Requirements and Associations With Geographic Clustering of Pertussis," found that "geographic pockets of vaccine refusal are associated with the risk of pertussis outbreaks in the whole community."

Another problem is that the DTaP vaccine likely doesn't work as well as the older DTP vaccine and likely doesn't work as well as we used to think it did. So instead of efficacy of 84 to 85%, as was once believed, it is likely closer to just 71 to 78%.

Other issues, including a decay in antibody to specific vaccine proteins over time, the possibility of an incorrect balance of antigens in the vaccine that could create a blocking effect, and genetic changes in the B. pertussis bacteria, could also possibly lead to increased vaccine failure rates.

California Pertussis Outbreak

Even though there were high rates of pertussis in 2005, the California pertussis outbreak of 2010 was really a wake-up call that whooping cough was coming back. In fact, it was just an outbreak, it was a full fledge epidemic.

There were 9,154 cases of pertussis in California in 2010, the most in 63 years, and 10 infants died.

Preventing Pertussis Outbreaks

Even if you are not in California, this outbreak should be a reminder of how serious pertussis infections are and the importance of pertussis vaccines. Keep in mind that in addition to completing the DTaP (Diphtheria, Tetanus, and acellular Pertussis) series of shots before starting kindergarten and getting a Tdap booster shot when they are 11 to 12 years old (or when they are older if they missed it), the Advisory Committee on Immunization Practices (ACIP) recommends that adults between the ages of 19 and 64 get a Tdap (Tetanus, Diphtheria, and acellular Pertussis) vaccine.

Adults who will have contact with infants less than 12 months old, including parents, grandparents over 65, child-care providers, and health care workers, should get a Tdap vaccine if they have not had one yet.

It is also recommended that pregnant women get a Tdap vaccine between 27 and 36 weeks gestation during each pregnancy to help protect themselves and their newborn baby from pertussis.

Symptoms of Pertussis

Since rates of pertussis are increasing with the California pertussis outbreak and in other areas of the country, it is important that parents be able to recognize the symptoms of pertussis.

Pertussis symptoms usually start just like regular cold symptoms about 6 to 21 days after being exposed to someone else with pertussis, often an adult with a chronic cough. These initial pertussis symptoms typically last a week or two and might include a low-grade fever, runny nose, congestion, sneezing, and a cough.

Next, just as you would be expecting a child's cold symptoms to be improving, the child with pertussis actually starts to get worse, and develops symptoms which can last an additional 3 to 6 weeks, including:

  • coughing spells or fits, which might end in the classic "whoop" sound
  • vomiting after coughing spells (post-tussive emesis)
  • cyanosis or blue spells after coughing
  • apnea or episodes where an infant actually stops breathing during or after a coughing spell

These pertussis symptoms then gradually improve over the next few months.

Parents should see their pediatrician if they think that their child might be developing pertussis symptoms or seek more immediate medical attention if your younger child has severe symptoms, such as apnea or prolonged coughing fits.

Pertussis Outbreaks 2012

California is not the only place seeing record levels of pertussis. Australia has also been seeing their highest pertussis cases since they began keeping records, reaching almost 30,000 cases last year and just over 23,000 so far this year.

As in California, there are areas of Australia where up to 8 to 18 percent of parents are refusing to vaccinate their children at all, and some health experts think that the Australian pertussis epidemic began in those areas.

The pertussis epidemic in California is over. They are back down to a state rate of less than 1.0 per 100,000 in 2012. Unfortunately, many other places are now seeing pertussis outbreaks, including:

  • Hillsborough County, Florida - 35 cases including a family with 6 unvaccinated children
  • Milwaukee County, Wisconsin - a cluster of 28 children at a private school and the death of a one month old in February
  • Bell, Waco-McLennan Counties, Texas
  • Polk County, Iowa - an increased number of cases in students, which prompted a vaccinated clinic in which 234 were vaccinated
  • San Luis Obispo County, California - two infants less than one month old have been found to have pertussis, an age that is at high risk for life-threatening infections
  • Cache County, Utah - an increased number of cases has been noted in the area, which many people will remember for their measles outbreak in unvaccinated children last year
  • Washington - which is experiencing a statewide epidemic of pertussis
  • Ravalli County, Montana - an outbreak is now up to 27 cases in the area and 115 unvaccinated children have been barred from coming to school for 21 days

With all of these pertussis outbreaks, it is important to keep in mind the words of Alfred DeMaria, Jr., M.D., who says in the article, "Accounting for Pertussis," that the "resurgence of pertussis and measles in the U.S. reminds us, once again, of the need to maintain high levels of population immunity."



California Department of Public Health. Number of Cases of Pertussis in California: Pertussis Summary Report (11-2-2010). Accessed November 2010.

CDC. Preventing Tetanus, Diphtheria, and Pertussis Among Adults: Use of Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular Pertussis Vaccine. MMWR. December 15, 2006 / 55(RR17): 1-33.

Jane Hansen. Whooping cough outbreak in Queensland as parents snub vaccination. The Sunday Mail (Qld). November 7, 2010.

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