UPDATE: This post has been updated as explained below.
In yet another sign of the perils and irresponsibility of the anti-vaccination movement, thousands of riders of the Bay Area Rapid Transit system are being warned that they may have been exposed to measles -- a disease that was declared eliminated in the U.S. in 2000 but has since returned.
The latest threat comes from an unnamed and unvaccinated UC Berkeley student who apparently contracted the disease while traveling in the Philippines during an outbreak there. Public health officials in Contra Costa County say people who rode BART during the morning or evening rush hours from Feb. 4 through Feb. 7 may have been exposed by the carrier, who is unidentified.
That could be hundreds of thousands of people. Health officials say those who have been immunized or have had the disease are probably still protected. But measles is highly communicable, and many unprotected individuals who came in contact with the source could become infected.
[UPDATE: The California Dept. of Public Health on Wednesday issued an advisory that 14 measles cases have been reported in the state so far in 2014. Of the 12 cases in which the patients' vaccination status is known, eight were unvaccinated--seven intentionally. The eighth is an infant too young to be vaccinated. The agency advises health professionals to be on the lookout. For more background, see this report by my colleague Eryn Brown.]
The Bay Area, as it happens, is a hotbed of anti-vaccination sentiment. Curiously, as Phil Plait points out on Slate, there's some correlation between affluent and well-educated communities and low vaccination rates. Marin County has one of the highest rates of "personal belief exemptions" for childhood immunizations, which of course endanger school mates and the community. At one Sausalito school, only 26% of entering kindergartners were vaccinated against measles. In Santa Cruz County, the rate of personal belief exemptions is a shocking 9.6%. (The state average is 2.8%, according to a report on KQED.)
The percentage of children in school or child care with all their required immunizations in Marin and Santa Cruz counties were among the lowest in the state outside of rural agricultural counties (83.5% and 79.7%, respectively). That's a public health crisis waiting to happen.
Measles is no joke in the developing world, where immunization rates are low. Untreated, it can cause pneumonia, neurological damage, or if contracted by pregnant women, birth defects in their children. The U.S. has experienced numerous troubling outbreaks since 2000 -- a total of 222 cases in 2011 and 189 last year, of which at least 15 were in California.
Most of those outbreaks originated with patients infected overseas, according to the Centers for Disease Control and Prevention. But their spread was attributable to "pockets of persons unvaccinated because of philosophical or religious beliefs," the CDC said. The point can't be stressed enough: People who spread anti-vaccination propaganda, and those who listen to them, are dangers to the community.