By then, measles had taken root. Last year, British public health authorities declared that measles was once again endemic. More than 1,300 measles cases in England and Wales were reported in 2008, the most in at least 15 years. Two measles patients have died since 2006. In California, some parents who have immunized their children expressed concern when told that their school had a significant percentage of students exempted from immunizations.
At Truman Benedict Elementary School in the Capistrano district, 27% of the kindergarten class in 2007 and 8% of kindergartners last fall had a personal-belief exemption on file.
Corrie Melcher, whose two sons attend the school, said she hoped their vaccinations would keep them safe.
"But it is a concern that children could be bringing those types of diseases into the classroom," she said.
Some parents who have chosen not to vaccinate, or agree to only some of the shots, said they did so after hearing about possible side-effects in the media, online and through other parents.
Julie Knights, a mother of three in San Clemente, said she gave her youngest, Cody, 5, only the shots she believed were absolutely necessary.
For example, she declined the vaccine for hepatitis B, a disease transmitted through infected blood or body fluids that can cause liver cancer and cirrhosis.
But Knights had Cody vaccinated for measles, mumps and rubella. She came to that decision after considering the possibility that her child could pass on rubella, also known as German measles, to a pregnant woman, resulting in brain damage or death to the unborn baby.
"I would feel socially responsible for that," she said.
Other parents said they feared autism and side effects more than the diseases.
"Is it life-threatening to get the measles . . . or is he potentially going to get a life-threatening reaction by getting the vaccination?" asked Sarah Bjorklund. She vaccinated her two school-age children on schedule but delayed shots for her youngest son. "I think you have to weigh what is the benefit of the vaccination versus the risk."
For Bjorklund -- whose children attend Stoneybrooke Christian Schools in San Juan Capistrano, where 18% of entering kindergartners had vaccine exemptions last fall -- doubts about vaccine safety resonate.
"Part of the reason is that there's been such a huge rise in autism . . . and what's the cause?" she said. "Just because the pharmaceutical companies say we need it doesn't mean we need it."
Public health experts say there is more than enough scientific proof that autism is not connected to vaccines and point out that many preventable childhood diseases can be deadly. Last year, a child whose parents had refused the vaccine for Hib, a type of bacteria, died in Minnesota, the first such death in that state since 1991. But they said it has been difficult to reassure skeptical parents.
"I think it's hard to unscare people," said Dr. Paul Offit, chief of infectious diseases at Children's Hospital of Philadelphia and a co-inventor of the rotavirus vaccine.
Times staff writer Doug Smith contributed to this report.