Herd, as in "herd immunity," the concept being that the majority of vaccinated people protect the minority who aren't vaccinated, a kind of safety-in-numbers for your immune system. But what if the number in the minority starts to creep up?
I blogged earlier this summer about a pertussis (whooping cough) outbreak in Rhode Island and a growing number of cases throughout the country (see the latest from the RI Dept. of Health). There were some indications then that the vaccine was losing its efficacy. But that may not be the full picture.
We’re seeing a few more cases of pertussis (whooping cough) in Rhode Island than usual right now (the total is eight as of Friday, July 20). But in the state of Washington, it’s reached official epidemic status. The Centers for Disease Control reports today in its weekly Morbidity and Mortality Report that, although the pertussis incidence rate is higher in Washington, there’s a national trend emerging in terms of what age groups are getting sick: