Jan. 4, 2010 -- Chickenpox cases have dropped by about 80% in the U.S. since a vaccine to prevent the disease became available almost 15 years ago, but many parents still reject immunization because of concerns about vaccine safety.
Now new research confirms what public health officials have long known: Children whose parents refuse to allow chickenpox vaccination are at increased risk for getting the disease.
From a group of close to 90,000 children enrolled in a Colorado health plan, researchers from the Kaiser Permanente Institute for Health Research in Denver identified 133 children who got chickenpox and compared them to 493 children matched for sex, age, and length of enrollment in the health plan who did not get the disease.
They found that children were nine times as likely to get chickenpox, also known as varicella, when their parents refused to have them vaccinated.
Overall, about 5% of chickenpox cases were attributable to vaccine refusal.
Seven children with chickenpox in the study (5%) were not vaccinated due to parental objections, compared to three (0.6%) without a history of chickenpox.
"Many parents refuse the varicella vaccine because they think of chickenpox as a mild illness, but this is not necessarily true," study investigator Jason M. Glanz, PhD, of Kaiser Permanente tells WebMD.
"Before the vaccine there were 100 deaths and 10,000 hospitalizations a year due to varicella. It can cause very severe illness in newborns and adults and in children with compromised immune systems."
CDC: Chickenpox Vaccine Is Safe
The CDC recommends that all healthy children who haven't had chickenpox should receive two doses of chickenpox vaccine, with a first dose optimally given between 12 and 15 months of age and a second dose given between 4-6 years of age (or at least three months later than the first dose).
Vaccination is also recommended for older children and adults who have no evidence of prior infection with the varicella zoster virus (VZV), which causes chickenpox.
The most common reactions from the vaccine are soreness or swelling at the site of the injection, or a mild rash or fever.
According to the CDC, more serious reactions such as seizure and pneumonia are very rare.
But several studies suggest that the VZV vaccine is the most commonly refused childhood vaccine.
It is not exactly clear how many parents choose not to have their children vaccinated.
"The best estimates we have suggest that about 1% to 2% of parents refuse vaccinations for their children, and there is evidence to suggest this number may be growing," Glanz says.
Infectious disease specialist William Schaffner, MD, says while the number of parents who reject all vaccines for their children remains small, the number with specific concerns about vaccines and vaccination schedules appears to be growing.
Schaffner is professor and chairman of preventive medicine at the Vanderbilt University School of Medicine in Nashville, Tenn.
"The pediatricians I talk to are telling me that the time they spend addressing parents' concerns about vaccinations has grown exponentially over the past five years," he says.
VZV Vaccine Very Effective
The VZV vaccine is almost 100% effective for preventing severe cases of chickenpox. Roughly one in 10 children who is vaccinated gets a milder case of the disease.
Vaccination is also believed to prevent the painful, nerve-related condition known as shingles, which is common among older adults and is also caused by the varicella zoster virus.
According to the National Institutes of Health, people who have been vaccinated against chickenpox appear to be less likely to get shingles later in life.
Schaffner says children who aren't vaccinated can have severe complications including bacterial infections and pneumonia if they get chickenpox.
And unvaccinated children are more likely to expose others who can't be vaccinated to the disease or are at high risk for severe chickenpox infection, including young infants, pregnant women, and people with weakened immune systems.
"We vaccinate the strong so that the weak are protected," he says. "Vaccination has always had two functions: to protect the individual and to protect the community."