Three years after an epidemic of whooping cough—largely eliminated from the general population for 53 years—struck 9,120 people in California in 2010 and killed 10 infants, researchers have blamed the outbreak on parents who refused to vaccinate their kids.
A study published Monday in the journal Pediatrics said that people who refused vaccinations for their children, largely for religious reasons, were 2.5 times more likely to be living in areas where whooping cough, also called pertussis, showed up. The disease is highly contagious and deadly, especially for infants, who cannot be vaccinated.
It doesn’t take a lot of people claiming a pertussis exemption in school for their kids to have an effect on the area. Scientists say that once fewer than 95% of people are vaccinated, a community loses “herd” immunity. Only 91% of California kindergartners statewide were vaccinated as of 2010, but researchers found that in some areas, as high as 84% of students received non-medical vaccine exemptions. (Some people cannot be vaccinated because of other medical issues.)
Blame for the outbreak of the bacterial infection wasn’t laid entirely on the exempted students. Pertussis appears in a cyclical fashion and the vaccine’s protection is now known to fade quicker than originally thought. So older kids are probably more susceptible, as are adults who didn’t receive a booster shot.
The California Department of Public Health reports that as of September 4, there have been 1,249 cases of pertussis in the state this year. That’s more cases than the 1,018 that were reported all of last year. The majority of cases (82%) this year involved children 18 and younger. No deaths have been reported. Santa Clara County had the most cases (192), followed by Marin County (122) and San Diego County (103). Nevada County has the highest rate of illness per 100,000 residents (72.3), followed by Marin (47.87).
Californians are free to skip vaccinations for religious reasons and don’t have to explain that is their reason. But last year, the state passed a law requiring parents who opt out to sign a document that verifies they understand the benefits of vaccines.
That benefit is being downplayed, and overshadowed by fear, among some groups that have decided that vaccines carry a high risk of causing autism and other serious maladies. There is no science to support that belief. But that level of ignorance is a prime mover behind new surges in diseases like measles, that had been pretty much eradicated.
Last year was the worst for whooping cough nationally since 1959. Texas, where the anti-vaccine movement has found marked success, is on a pace to register the most pertussis cases since the 1950s. Last month, a measles outbreak in that state prompted an outcry for parents to get their kids vaccinated.