by Todd Neale
Children whose parents refuse vaccinations for them provide fertile ground for the spread of vaccine-preventable diseases, an investigation of a 2008 measles outbreak in San Diego demonstrated.
Although the rate of two-dose immunization against measles was 95% in the area, a single case of measles from a 7-year-old child returning from overseas sparked an outbreak that exposed 839 people and sickened 11 other children, according to David Sugerman, MD, MPH, of the CDC’s Epidemic Intelligence Service, and colleagues.
None of the 12 children, who ranged in age from 10 months to 9 years, had been vaccinated — nine because their parents had refused the vaccine and three because they were too young, the researchers reported in the April issue of Pediatrics.
Although the virus was not spread extensively, it came at a substantial cost of $176,980 for investigation, containment, and healthcare.
In San Diego, the overall rate of vaccine refusal — predominantly because of safety concerns — was low at 2.5% in 2008, but it had been rising since 2001.
The possibility that increasing rates of intentional undervaccination could lead to a rise in outbreaks of vaccine-preventable diseases is “a monumental concern,” according to Anne Gershon, MD, a pediatric infectious disease expert at Columbia University Medical Center in New York City.
“It’s very important for parents to understand that the disease itself is always more serious than a true reaction to the vaccine,” she said in an e-mail.
The endemic transmission of measles was declared eliminated in the U.S. in 2000 because of widespread use of an effective vaccine, but the virus remains endemic in other parts of the world.
Occasionally, imported cases cause outbreaks. In 2008, there were 140 measles cases in the U.S., the largest number since 1996, when there were 508.
There are concerns that cases of measles and other vaccine-preventable diseases will continue to increase as public focus shifts from the dangers of disease to vaccine safety.
To explore the effect of intentional undervaccination on an outbreak of a vaccine-preventable illness, Sugerman and his colleagues turned to the January 2008 measles outbreak in San Diego, sparked by a 7-year-old returning from a trip to Switzerland.
The child’s parents had signed a personal-beliefs exemption to refuse vaccination for their children.
The index patient directly infected his two siblings, two classmates, and four children who were treated at the same clinic.
The index patient’s sister then infected two of her classmates. One of the index patient’s classmates infected his brother, bringing the total number of cases to 12.
One child, a 10-month-old, was hospitalized, and received IV hydration for diarrhea.
A vigorous public health response, including quarantine of exposed children who had not been vaccinated, prevented the outbreak from progressing further.
In the study area, parents who refused vaccines for their children tended to be white, well-educated, and from the middle and upper classes.
There were clusters of vaccine refusal, occurring more often in public charter and private schools, as well as in public schools in upper-class areas.
William Schaffner, MD, chair of preventive medicine at Vanderbilt University in Nashville, said in an interview that there is growing concern about these community clusters, because they create a pool of susceptible children who interact with each other on a daily basis.
Although high vaccination rates prevented the San Diego measles outbreak from extending into the general population, Schaffner said “you cannot rely upon herd immunity to protect each and every child.”
In discussion groups and surveys, most parents who refused vaccines for their children were concerned about possible adverse effects, including autism, ADD/ADHD, asthma, and allergies. They expressed skepticism about the government, pharmaceutical industry, and medical community.
In addition, “they believed vaccination was unnecessary, because most vaccine-preventable diseases had already been reduced to very low risk by improvements in water, sanitation, and hygiene and were best prevented by ‘natural lifestyles,’ including prolonged breastfeeding and organic foods,” Sugerman and his colleagues wrote.
But, according to Schaffner, parents harboring those ideas are misguided.
“There’s nothing in that sentence that is correct,” he said. “You can have the purest water, eat the most natural food, be very healthy, and if exposed to measles, your child will get measles and can get a very severe case.”
He noted that people often forget that before vaccination was introduced in the U.S. in 1963, measles killed an average of 400 children a year in the U.S.
“People don’t recognize how potentially very serious these so-called childhood infections can be,” he said.
The best way to help inform parents about the importance of vaccination for their children remains the dissemination of science-based information through the media and doctors, Schaffner said, although he acknowledged that that approach does not seem to be working.
A longer-range solution, he said, would be to make sure school health curricula contain lessons on vaccines and the diseases they prevent. Schaffner said many current curricula are deficient in this area.
“We shouldn’t be surprised that when these teenagers in a few years become young adults and parents that they’re not very educated about vaccines.”
Todd Neale is a MedPage Today staff writer.