OVER THE PAST HALF CENTURY VACCINATIONS HAVE nearly eradicated a number of infectious diseases, including polio, diphtheria, and measles in developed countries. But in the past decade some of these diseases have reappeared, particularly pertussis (whooping cough) and measles. In 2014, there were nearly 10,000 pertussis cases reported in California, more than had occurred in any year since 1947, and over 200 of the hospitalized patients were infants under four months of age. In December 2014, an outbreak of measles occurred at Disneyland in Southern California that spread across the state and nationally. The measles virus is extremely contagious and can lead to severe brain disease, seizures, ear or chest infections, and even death.
These outbreaks of disease have occurred primarily in regions of California where vaccination rates have fallen below the herd immunity level (the level of inoculation required to protect a population against a disease). In California and many other states as well, there has been an increase in the number of families that obtain a “personal belief” exemption permitting them to withhold their children from vaccination programs. The high number of these exemptions accounts for a rising incidence of diseases that strike children disproportionately and that are often severely injuring or even fatal. In the case of the Disneyland measles outbreak, for example, scientists from M.I.T. and the Boston Children’s Hospital who analyzed the data reported that vaccination rates for the exposed population had fallen to between 50 and 86 percent, far below the inoculation level of 95 to 99 percent that is needed for herd immunity.
Alarmed by this upsurge of vaccine-preventable diseases, a group of parents contacted state legislators about tightening up California’s vaccination requirements. State Senators Richard Pan and Ben Allen drafted SB 277, a bill that eliminates the personal belief exemption that allowed unvaccinated children to attend school. Since it is in a school environment that infectious illnesses are most commonly transmitted from one child to another, private as well as public schools fall within the scope of the bill. SB 277 still allows exemption from vaccination for a medical reason—a child’s allergy to a vaccine, for example—but exemption is no longer granted to families that object to vaccination on religious or philosophical grounds or because they believe it is unsafe.