Kids who get chickenpox may be less likely to develop atopic dermatitis and asthma when they're older than their peers who don't get chickenpox - including those that are vaccinated against it, suggests a new study.
But vaccine experts warn that the study was limited, and that one finding shouldn't challenge the benefits of the chickenpox vaccine.
Atopic dermatitis is a type of eczema, often causing itchy rashes, that arises from an allergic reaction. It may also be the "first step" in a series of allergies that leads to asthma, said the study's lead author, Dr. Jonathan Silverberg, from the State University of New York Downstate Medical Center in Brooklyn.
Previous research by Silverberg and his colleagues on the body's response to chickenpox and shingles, a related skin condition, suggested that getting chickenpox could decrease a child's risk of later developing atopic dermatitis. To test this hypothesis, they examined the medical records of almost 700 children and adolescents, some with atopic dermatitis and some without the bothersome skin condition.
For each subject, the authors looked back in the records to see if they had ever been infected with chickenpox.
Kids who had chickenpox — especially those who had it when they were young - were significantly less likely to get atopic dermatitis later, according to the results, which are published in the Journal of Allergy and Clinical Immunology. Among kids who eventually were diagnosed with atopic dermatitis, 20 percent had previously gotten chickenpox, compared with 28 percent of kids without atopic dermatitis.
The link went away for kids who had chickenpox when they were older than 10 - they were just as likely to get atopic dermatitis as other older kids who never had chickenpox.
Kids who had chickenpox were also less likely to be diagnosed with asthma after getting the virus.
Being vaccinated against chickenpox did not seem to give kids any protection against atopic dermatitis or asthma.
While "cost-effective" studies have shown that it makes economic sense to vaccinate kids against chickenpox, those studies haven't factored in the possibility that preventing kids from getting chickenpox might mean more will end up with atopic dermatitis or asthma, the authors say.
They argue that if further research confirms their findings, waiting to vaccinate kids against chickenpox until they are older (8 or 10 years old) could make the vaccine more cost-effective and prevent some cases of atopic dermatitis and asthma.
According to the CDC, the chickenpox vaccine costs about $70 to $80 per dose.
Kids are currently vaccinated at age 1, Seward said, and there's a good reason for that - because most kids who get chickenpox get it when they're very young, she said. Kids in this study who got chickenpox were an average of 3 years old when they were infected.
While chickenpox is often not viewed as very serious, Seward said, some kids do end up with pneumonia or other serious infections, and some lose limbs.
"Upfront you don't know, is this going to be a case of itchiness and fever for a couple days, or is this very serious?" she said.
Dr. Eugene Shapiro, an expert on the vaccine and a professor at Yale University School of Medicine in New Haven, Connecticut, said that before the vaccine was introduced, 12,000 people were hospitalized every year for chickenpox and 120 died.
Silverberg agreed that pushing back the age kids are vaccinated could mean more deaths from chickenpox. Allowing for increased chickenpox infections in childhood could decrease "herd immunity" — where the level of immunity in the whole population is high enough to prevent large outbreaks of an infection - "and may place some adults at risk for getting the disease," Silverberg told Reuters Health in an email.
Still, he said, more chickenpox might mean less asthma - another potentially fatal condition.
Dr. David Kimberlin, who studies pediatrics and infectious diseases at the University of Alabama at Birmingham, cautioned about taking too much away from a study that looked back at medical records, rather than one that started with a group of kids and followed them for a number of years.
Seward noted that the study didn't take into account other factors known to affect atopic dermatitis, such as family history and other allergies - something that's hard to do with a study set up in this way, she said.
Silverberg said that looking back at records was useful because it would be hard to find lots of kids with chickenpox now, given the vaccination program.
He also said that more research - possibly including studies at the state or national level - is needed before he would recommend any changes in vaccination policy. Those studies would need to look broadly at the link between chickenpox infection and atopic dermatitis and include the costs of atopic dermatitis and asthma in the analysis of the vaccine's cost-effectiveness, he said.