Editor’s note: This article was updated at 1:18 a.m. to include additional information about the number of pertussis vaccinations that Vermont children have received this year.
Whooping cough, or pertussis, is spreading across Vermont at a record rate this year, with 310 cases confirmed so far. As that number continues to climb, however, a clear-cut remedy is nowhere in sight.
Officials at the U.S. Centers for Disease Control and Prevention (CDC) say the best way to prevent pertussis is to get vaccinated. But data from the Vermont Department of Health (DOH) suggest that going through the pertussis vaccination regimen is not a sure-fire way to ward off the highly contagious disease.
As of Aug. 10, there were 178 confirmed cases of pertussis in Vermont children between the ages of six months and 18 years. Of that number, 90 percent — or 160 kids — had received at least one dose of the child vaccination, while the majority had received five or six doses. According to the DOH, one child had received one or two doses, eight had received three doses, nine had received four doses, 74 had received five doses and 68 had received six doses.
The DOH recommends that all kids under the age of 7 receive five doses of the vaccine known as DTaP, or the diphtheria, tetanus and acellular pertussis vaccine. The DOH calls for children to receive four doses before 18 months of age and another before kindergarten.
The problem with DTaP, as a study published last month in the New England Journal of Medicine shows, is that the vaccine loses its effectiveness. The study compared 277 children, ages 4 to 12, and found that a child’s odds of contracting pertussis increased 42 percent every year after the fifth dose.
Patsy Kelso, a DOH epidemiologist, said the vaccination regimen isn’t producing the desired results.
“The current thinking is that the pertussis vaccination is just not as effective as we’d like it to be,” she said. “Even if you’re vaccinated, it’s efficacy wanes after a few years. Although no vaccine is perfect, this vaccine is less good than we’d like.”
In addition to DTaP, there’s a pertussis vaccine called TDaP, which stands for the tetanus, diphtheria and acellular pertussis vaccine. Kelso said that before kids enter seventh grade, they should receive an injection of TDaP. She advised that adults and some senior citizens over the age of 64 should receive the vaccination, too.
According to the CDC, TDaP is even less effective than DTaP. U.S. officials estimate that the vaccine protects only seven out 10 people. Officials believe that DTaP has an efficacy rate of 80 percent to 90 percent during and right after the five-shot process. After five years, they estimate, the efficacy rate drops to 70 percent.
While Kelso acknowledged that the rise in documented pertussis cases is partially due to a new method used for testing the illness, she said Vermont’s record outbreak this year is not just a matter of calculation.
“In Vermont we started doing a new lab test for pertussis this year and it’s a lot more sensitive than the tests we used to do,” she said. “Even without that, though, there’s still an increase in cases.”
And it’s not just Vermont; every state but Michigan and California have experienced outbreak levels at least twice as high as those recorded by the CDC at this time in 2011. As of the 39th week of 2011, the CDC had recorded 11,969 pertussis cases. That number has nearly tripled this year, as officials have documented 30,908 cases.
In 2012, there have thus far been more cases of pertussis than in any full calendar year recorded since 1959, when roughly 40,000 cases were reported. The last time Vermont saw pertussis cases near this year’s level was in 1997 when 283 were reported. In 1996, 280 cases were reported.
As of Sept. 20 of this year, Vermont had the sixth highest incidence rate in the country, with 42 people per 100,000 contracting pertussis. Wisconsin had the highest incidence rate in the country at 78.6, then Minnesota with 63.5 and Washington with 58.1. The national average is 9.3 people per 100,000.
Kelso said that the current thinking among health officials is that this widespread uptick in pertussis is due to the vaccinations faltering. Nonetheless, she said, the vaccination can help fight off the illnesses when contracted, just as the flu vaccine can.
“We don’t say that it’s necessarily failing people because they might have less severe symptoms,” she said. When asked if she could quantify this observation, she said she couldn’t.
Despite the vaccination’s less-than-perfect track record, Kelso maintains that it’s better to get vaccinated than to not. Furthermore, it’s free.
“In Vermont, we provide no cost vaccines for all children and adults. So people should see their primary care providers because if their primary care providers are enrolled in our program, they get free vaccines.”
For those Vermonters without a primary care provider, Kelso said to contact a local health department office to learn about the numerous ways to obtain free vaccinations.
“The best thing is to get vaccinated,” she said. “And if children have a cough they should not go to school or child care. They should be seen by a health care provider.”