Last year, a record 81 cases of pertussis were reported in Washtenaw County -- by far the highest number since electronic records have been kept, and far higher than the previous record set in 2003, when 36 cases were reported. Statewide, over the last year, the number of whooping cough cases has almost doubled. As always, infants are most at risk of hospitalization or death; but across the state, teenagers and grownups were most often affected by pertussis, probably because they'd missed their Tdap booster shots.
And the problem isn't limited to Michigan. So far this year 6 infants, all less than 3 months old, have died in California, in what looks like its worst whooping cough epidemic in 50 years -- with about 1,500 reported cases. Before this, South Carolina was the only other state where whooping cough cases have exceeded the "epidemic threshold" -- a statistical measure that means there are significantly more cases than usual for the time of year.
California health officials have announced a broadened vaccination campaign for teens and adults. Anyone in contact with babies has been urged to get the vaccine, even senior citizens and pregnant women. That's important because infants get 3 doses of the vaccine, but they aren't fully protected till after they're 6 months old. And it's important because neither the pertussis vaccine nor natural infection gives a person lifelong immunity to whooping cough. Outbreaks tend to occur in 5 year cycles, when immunity wanes.
Indirect evidence suggests that refusal to vaccinate children may play a role in these epidemics. Most pertussis cases occur in areas where the parents exempt their children from routine vaccination -- a choice that California state law allows. Marin County north of San Francisco has a high rate of vaccine refusal, and the highest number of whooping cough cases this year. Another, 2008 study, matched whooping cough outbreaks in Michigan with geographic pockets of families that exempted their children from school immunizations. Again, fewer vaccinations corresponded with more pertussis.
July, August, and September tend to be peak months for whooping cough. For their own benefit, and for their children's sake, parents, grandparents, and other caretakers in contact with infants should make sure their vaccinations are up to date.