“What’s the matter with Vermont?” was the provocative headline in Slate.com late last week. It suggested that Vermont, that lovely Blue but, to some, eccentric state, was up to some of its liberal tricks or behaving irrationally. But the topic, with the subhead “Anti-vaccine activists derailed a bill that could have blunted the whooping cough epidemic,” leveled a serious accusation: that the pertussis epidemic afflicting Vermont over the last few years could have been mitigated had more children been vaccinated for whooping cough and had the philosophical exemption been disallowed, as legislation introduced last year intended.
In her article Helena Rho, a former assistant professor of pediatrics who has taught at Children’s Hospital of Philadelphia, characterized Vermont — which had the second-highest rate of pertussis cases in the nation during 2012: 100.2 per 100,000 persons — as a state where parents’ resistance to vaccinating their children has contributed greatly to putting more people at risk for the disease. What’s more, the article states that “[i]n parts of Vermont, the vaccination rate is only 60 percent.”
But National Immunization Survey reports for children 19 to 35 months and 13 to 17 years old showed Vermont with rising percentages of infants and toddlers getting all four recommended doses of the diphtheria/tetanus/acellular pertussis (DTaP) vaccine — up from 83.2 percent in 2009 to 88.2 percent in 2011. (This compares to 84.6 percent nationally.) Among adolescents getting the Tdap booster, the rise has been from 87 percent to 90.1 percent. In addition, the Vermont Health Department reports that 93 percent of children entering public school kindergarten are up to date on the DTaP — one more shot is given between age 4 and 6 for a total of five — and 91 percent of children entering seventh grade are up to date. (Private school rates are lower: 83 percent in young children and 86 percent for children entering seventh grade.)
In terms of the rates of immunization, there appears to be nothing “the matter with Vermont.” Vermont Department of Health immunization program director Christine Finley, noting the rise in immunization rates for most vaccines over the last three years, points to a different issue — something the Slate article refers to almost in passing — the evidence that the effectiveness of the acellular vaccine for pertussis now in use declines quite rapidly. The CDC reported last May that measures of Tdap effectiveness within a few years of getting the shots ranged from 66 percent to 78 percent, less than had been expected in pre-licensure trials.
The acellular vaccine was developed in the late 1990s in response to what some saw as too many severe side-effects of the whole-cell vaccine, the DTP, that had been in use since the 1940s and which had reduced annual cases from more than 250,000 at one time to a few thousand a year. Since the 1980s epidemiologists have seen increases, but within a few years of the introduction of the acellular vaccine, these increases were even more apparent and by the mid-2000s epidemics were in full swing, leading to the current spate of research into the causes of waning immunity and into effective methods for once-again controlling whooping cough.
There has been some success in reducing cases. Studies such as one done in Washington state after whooping cough cases increased 1,300 percent from early 2011 to mid-2012 showed that once the Tdap booster was given, adolescent infection rates dropped off. And pertussis is known to increase suddenly, as it did in California a few years ago, and as it has done since 2010 in Vermont, and then diminish. It does, however, still threaten infants especially. Most deaths from pertussis are in infants. All countries vaccinate against pertussis.
The recommended schedule is now five vaccinations by school age — four for infants and toddlers and one in the 4-to-6-year-old age span. However, in September 2011, facing reports of increasing numbers of children who were not getting the full five doses, the American Academy of Pediatrics (AAP) and the Centers for Disease Control (CDC) recommended the Tdap booster be given at age 7 to 10 rather than 11 or 12, if a child has not had the full five DTaP series by that time. (At the same time, they recommended a Tdap shot for those 65 and older who have contact with infants, since those too young to be vaccinated are most at risk for infection, complications and death. Most of the 4,298 infants reported with pertussis in 2010 required hospitalization.)
The immunology community is straightforward in acknowledging that there is currently, as CDC researcher Dr. Thomas A. Clark and co-authors wrote in a May 2012 paper for Trends in Microbiology, an “incomplete understanding of the immune response to infection and to vaccination.” While some vaccines are much more effective than the pertussis vaccine — and, history shows, some diseases can be wiped out — even getting whooping cough does not confer lifelong immunity, which is why adult immunization is now recommended. But the researchers see limitations to the current pertussis vaccine series, even if regular boosters are administered. What has not changed in the scientists’ understanding of how to fight the disease: herd immunity is the key.