Nov. 28, 2011 -- Chickenpox infection can be life-threatening for infants who are too young to receive the chickenpox vaccine. The good news is that the routine vaccination of children aged 1 and older has shown spillover benefits for infants.
The U.S. began recommending a single dose of the chickenpox (varicella) vaccine for children aged 12 months and older in 1995. A second dose was added to the immunization schedule in 2006.
Before the vaccine was recommended, infants were four times more likely to die from chickenpox compared to children aged 1 to 14.
There has been close to a 90% drop in the rate of chickenpox among infants from 1995 to 2008, even though they are not eligible for the vaccine.
"Vaccinating children aged 12 months and older protects infants who are too young to be vaccinated," says study researcher Adriana S. Lopez, MHS. She is an epidemiologist at the CDC in Atlanta.
Lopez and colleagues analyzed chickenpox rates and severity among infants aged 0-5 months and 6-11 months from 1995 to 2008. Their goal was to find out some of the indirect benefits of routine chickenpox vaccination in the U.S.
The study is published in Pediatrics.
The researchers found the viral infection was actually milder among infants aged 0-5 months, compared with those aged 6-11 months.
This is likely because younger infants are still benefiting from maternal antibodies to chickenpox. These protective antibodies do wane over time.
Protecting Infants From Chickenpox
There have been major strides against chickenpox, but we can't afford to become complacent, Lopez says. "Even though the number of cases has gone down, there are still cases out there," she says. "It is important to have high vaccine coverage with the recommended two doses so that the risk is low for infants and others who can't get vaccinated."
"This is very good news," says Gail Demmler-Harrison, MD. She is a professor of pediatrics at Baylor College of medicine in Houston. Most people think of vaccines as benefiting only the person who receives the shot, she says.
But "this study shows that there are lesser-appreciated secondary benefits to the chickenpox vaccine, namely protecting vulnerable young infants," Demmler-Harrison tells WebMD.
This concept is known as herd immunity, where enough people in a community get vaccinated to reduce the spread of a disease like chickenpox or measles.
At first there was some pushback by parents about the chickenpox vaccine, she says. "It had been difficult to get off the ground because the prevailing point of view was that chickenpox was a benign, inconvenient rite of passage of childhood."
But, "among infants, chickenpox can be a really serious disease," Demmler-Harrison says. "The vaccine was finally embraced and we are seeing real benefits." Pregnant women, the elderly, and people with compromised immune systems are also at risk for severe complications from chickenpox.
Jeffrey Brosco, MD, PhD, sums up the new findings this way: "Vaccinating 1-year-olds protects the next baby." He is a professor of pediatrics at the University of Miami Miller School of Medicine.