Every month, California normally sees between 80 and 100 cases of pertussis—more commonly known as whooping cough. That’s changed in just the last two weeks, though. In the first half of June, there have been 800 cases.
California isn’t alone; the CDC reports that pertussis cases are up by 24% across the country. For older children and adults, the illness is debilitating, but manageable and often ultimately recoverable. But infants face a different set of statistics. About half of infants one year old or younger with pertussis are hospitalized, and 1-2% of those die. Two infants have already died this year in California.
Pertussis works by disabling the respiratory system’s self-cleaning mechanism, the millions of tiny hairs called cilia that normally sweep mucus and other debris out of the airway. The bacteria that causes whooping cough, Bordetella pertussis, secretes a toxin that paralyzes those cilia. With the cilia out of commission, mucus and debris build up in the airways. Clogged airways lead to coughing fits, which—because the bacterial toxin also causes inflammation—are followed by a telltale “whoop” as the patient tries to catch her breath.
It’s an exhausting cycle that can go on for weeks and often causes pneumonia or other respiratory problems. But it’s also easily preventable. The Tdap vaccine, which also protects against tetanus and diphtheria,.is highly effective—fully protecting around 80-90% of children who receive it. But pertussis still has some opportunities to sneak in.
Monte Morin, writing for the L.A. Times:
The earliest age an infant can be vaccinated is six weeks. Because of this, health officials say every pregnant woman should get a Tdap vaccination in the third trimester of pregnancy, as the mother’s immunity will transfer to her baby — at least temporarily.
Unlike the measles vaccine, pertussis vaccines do not provide lifelong immunity. It’s partially for this reason that whooping cough is cyclical: It reaches epidemic levels every three to five years.
Those three-to-five-year outbreaks have been getting more and more severe in the last decade. The Tdap vaccine, introduced in 2005, has a lower risk of side effects than the older form of the vaccine but doesn’t seem to last as long. New strains of whooping cough could also be contributing to the increase.
But a third possibility, and one that’s becoming increasingly common, is that lower immunization rates in certain communities are eroding the vaccine’s ability to prevent an outbreak.
Whooping cough is so contagious that more than 90% of a population must be vaccinated to keep it from spreading. Statewide vaccination rates in California approach that level, but there are certain communities—especially in affluent, highly-educated areas—where the majority of school-age children aren’t immunized. In 2010, the year of California’s most recent epidemic, a study published in Pediatrics showed that the likelihood of a pertussis outbreak spiked near those communities.
More than 9,000 cases—and ten deaths—were reported in California in 2010. If this year’s epidemic maintains its current pace, it will match those statistics.