Once vaccination rates dip below a certain point, outbreaks of childhood diseases can spread quickly.
Last year, Hilary Chambers, a San Diego radio host and mother of a baby girl, saw firsthand how fast measles can be passed among children.
A 7-year-old boy brought back a case of the disease from Switzerland and infected his two siblings and nine other children at his public charter school and doctors' office. One of those children, a 10-month-old boy too young to be vaccinated, went to day care with Chambers' daughter Finlee.
Public health officials informed Chambers that her daughter was at risk for contracting measles. Finlee had just turned 12 months old, meaning she was eligible for her first measles shot, but that inoculation appointment hadn't yet been scheduled. Chambers was told that she needed to keep Finlee quarantined at home, 24 hours a day, for three weeks.
"So I totally freaked out," Chambers said. "The child at our day care that contracted measles was hospitalized with a 106-degree fever."
Finlee was one of about 70 children who were quarantined in the case.
According to the U.S. Centers for Disease Control and Prevention, measles caused 450 deaths and 4,000 cases of encephalitis in this country each year before a vaccine became available in the mid-1960s.
Measles can be particularly dangerous for infants, because it can lead to pneumonia and even inflammation of the brain.
Knowing how sick her child's day care companion had become, Chambers and her husband were very worried. They took turns taking time off work so they could monitor her constantly. In the first week, public health officials called every day to make sure they weren't violating the quarantine. Every small cough prompted a flood of concern.
After about a week, Finlee had no signs of illness. She still had to stay home for the rest of the three-week quarantine.
Chambers said she did not blame the parents of the 10-month-old boy; after all, he was too young to get the measles vaccine. By the time he returned to day care a month later, he had lost weight, and some of his hair had fallen out. He was lethargic.
Many parents at the day care center voiced anger and frustration at the parents of the boy with measles, she said. The parents had taken their unvaccinated children to Switzerland, which has been undergoing measles outbreaks since 2006. (Measles outbreaks have continued to occur this year.)
Public health experts said the virus was able to spread to others in part because the boy attended San Diego Cooperative Charter, where 10% of students had exemptions for vaccines, a rate at which the risk for outbreaks is deemed high.
Chambers, who is inoculating her daughter despite some concerns about vaccine safety, says parents should have the right to choose whether their children are immunized. But she said that choice does have consequences.
"If you decide to put the greater community at risk by choosing not to vaccinate, there are huge responsibilities that go along with that," she said. "Do you home-school your kids? Do you not take your kids to countries where there's a higher incidence of these diseases?
"I think you need to adjust your family's lifestyle accordingly, because you are putting the greater community at risk. So don't just not vaccinate and live like everything's normal, because it's not."