Ever since the 2010 California pertussis outbreak, in which there were 9,154 cases of pertussis, the most in 63 years, and 10 infants died, many people, especially parents, are wondering why we are seeing more pertussis these days.
Is it because the pertussis vaccines simply don't work, as the anti-vaccine movement would have you think?
Or is it because there are higher rates of unvaccinated kids these days and parents using alternative immunization schedules, instead of the standard immunization schedule from the CDC?
A new commentary that will appear in the May issue of Pediatrics, "Why Do Pertussis Vaccines Fail?," may finally give us some answers.
While the title of the article might have you think that all of the blame lies with the pertussis vaccines, that certainly isn't the case. While there can be vaccine failures with the pertussis vaccines, just like any other vaccine, that doesn't mean that the vaccine doesn't work for most children.
One of the problems 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.
So it isn't that the pertussis vaccine doesn't work. That should be easy to see when you look at the pertussis rates in California, when the highest rates by far were in infants less than 6 months of age (434 per 100,000 people). In contrast, children who were 6 months to 6 years old had a rate of only 62 per 100,000.
And the results of a study that were presented at the 49th annual meeting of the Infectious Diseases Society of America in Boston show just how important the pertussis vaccine is, as:
- vaccine effectiveness was 98.1 percent among children who received their 5th dose within the past year
- long term effectiveness - children who were five or more years past their last DTaP dose - was about 71 percent
- 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
It is also important to note that the high rates seen in 2010 in California are still well below the rates that were seen in the prevaccination era, when the attack rate of pertussis in the United States was as high as 157 per 100,000 people, with about 200,000 cases a year.
What's the answer? It certainly isn't for more kids to follow alternative immunization schedules or to simply skip vaccines all together. Natural immunity isn't going to keep newborns and infants from getting pertussis, the ages which are most at risk for life-threatening infections, as they catch pertussis from people around them, including those working on their natural immunity. Natural infections don't even provide life-long protection against pertussis, as some people believe. That natural immunity wanes fairly quickly too.
The future of pertussis control more likely is going to be in maximizing our current vaccination program, including getting more teens and adults to get the Tdap vaccine. According to the CDC, in addition to protecting yourself and those people around you, "people who do catch whooping cough after being vaccinated are much less likely to be hospitalized or die from the disease."
Unfortunately, children who aren't vaccinated against pertussis can't "hide in the herd" and rely on the rest of us who do vaccinate our children to provide them with protection. Instead, since they are at a higher risk, they get pertussis and get the rest of us sick.
In a 2009 study that appeared in Pediatrics, researchers found that "vaccine refusers had a 23-fold increased risk for pertussis when compared with vaccine acceptors, and 11% of pertussis cases in the entire study population were attributed to vaccine refusal." And since pertussis is highly contagious, with every primary case typically infecting as many as 17 other people, it makes sense that higher rates of children using vaccine exemptions could be at least one of the factors in these outbreaks.
In fact, one 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."
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
And although it didn't make the news, the Dallas County Health Department informed me that a local newborn died of pertussis this month.
Why so many pertussis outbreaks? While experts continue to work on that question, my only real question is why are so many parents still not vaccinating their children?
As Alfred DeMaria, Jr., M.D. says in the article, "Accounting for Pertussis," the "resurgence of pertussis and measles in the U.S. reminds us, once again, of the need to maintain high levels of population immunity."