Pediatric Infectious Diseases Society
Since the chickenpox vaccine became available in the U.S. in
1995, there has been a large reduction in chickenpox cases.
Hospitalizations
and outpatient visits for chickenpox have continued their decline after a
second dose of the vaccine was recommended to improve protection against the
disease, according to a new study published in the Journal of the
Pediatric Infectious Diseases Society.
The findings also suggest that
increasing vaccination coverage against the once common childhood illness helps
protect those who are not immunized themselves.
Before the vaccine was available in the U.S. in 1995, about 4
million people would get chickenpox nationwide each year, according to the
Centers for Disease Control and Prevention (CDC). Nearly 11,000 people were
hospitalized annually, and 100 to 150 people died. A second dose of the vaccine
was recommended in 2006.
In this latest study, CDC researchers Jessica Leung, MPH, and
Rafael Harpaz, MD, MPH, drawing on national health care claims data from 1994
to 2012, found that there were 93 percent fewer hospitalizations for chickenpox
in 2012 compared to the period before the vaccine was introduced.
During the
two-dose varicella vaccination period (2006-2012), hospitalizations declined 38
percent. Outpatient visits for the illness also dropped significantly. There
were 84 percent fewer outpatient visits in 2012 versus the pre-vaccination
period. During the two-dose varicella vaccination period (2006-2012),
outpatient visits declined 60 percent.
"We found that, in our study, rates for varicella in the
U.S. continued to decline as the varicella vaccine program has become fully
implemented," said Leung, the study's co-author. "We saw significant
declines in rates of varicella after the one-dose vaccine was recommended in
1995 in the U.S., and we're continuing to see additional declines in varicella
after two doses were recommended in 2006."
The largest declines were among children and adolescents 1 to 19
years old, a population targeted for vaccination against chickenpox. But the
researchers also saw substantial declines in outpatient visits and
hospitalizations among infants younger than 12 months, for whom the vaccine is
not recommended, and in adults, who are often not immunized, suggesting the
possibility of herd immunity.
"The surrounding population that can be
vaccinated are not getting sick, and therefore the data suggest that these
infants are also being protected," Leung said. "We're seeing that for
adults as well."
The study also found a considerable rise--from 6 percent in 2003
to 17 percent in 2012--in the proportion of outpatient visits for chickenpox in
which patients were tested for the disease.
The authors noted that lab testing
will become increasingly important for distinguishing chickenpox from other
similar rash conditions as cases of chickenpox continue to decline and health
care providers become less familiar with its clinical presentation, and the
increasing proportion of chickenpox cases among people are who are vaccinated,
which are typically mild and difficult to diagnose based on symptoms alone.
