TUESDAY, Oct. 8 (HealthDay News) -- Two doses of chickenpox
vaccine are better than one, new research confirms.
After the introduction of the second dose of chickenpox vaccine,
the rates of chickenpox infection dropped 76 percent and 67 percent
at two U.S. sites tracked for the study on opposite sides of the
Rates of infection in adults and infants -- two groups who
generally don't receive the vaccine -- also went down, suggesting
that higher levels of immunity in the population are decreasing the
amount of circulating chickenpox.
"The first dose of vaccine was highly protective for reducing hospitalizations, deaths and other severe complications, but it wasn't fully protective against mild disease. There were still mild breakthrough cases, and these people could transmit the disease to those who hadn't been vaccinated," said Dr. Rachel Civen, senior study author and a medical epidemiologist with the Los Angeles County Department of Public Health.
"In 2006, it was recommended that a second dose be given between the ages of 4 and 6. And, we've seen a continuous significant decline since then, and the drops are across all age groups. The transmission is less throughout the whole community," she said.
Results of the study were published online Oct. 7 and in the
November print issue of
Chickenpox, which is also known as varicella, is a highly
contagious viral disease. Before the varicella vaccine was
introduced in the United States in 1995, about 4 million people had
the chickenpox each year, according to the U.S. Centers for Disease
Control and Prevention.
Although many people tended to think of chickenpox as a
relatively mild infection, it caused more than 10,000
hospitalizations each year and about 100 deaths annually, according
to background information in the study.
After the vaccine was introduced in 1995, the incidence of
chickenpox went down by 90 percent and deaths from the disease
dropped by 88 percent, but there were still outbreaks occurring.
That's why experts decided to add the second dose in 2006.
The current study was designed to see how well the second dose
of vaccine kept chickenpox under control. It included two sites --
one in Antelope Valley, Calif., and the other in West
Infections in these sites dropped dramatically between 2006 and
2010. The Antelope Valley site had 76 percent fewer cases of
chickenpox in 2010 than they did in 2006. West Philadelphia saw a
67 percent decline in the same time period. Both sites had a 98
percent decline in the incidence of chickenpox from 1995 to
Of those who came down with chickenpox between 2006 and 2010 in
the study sites, just 7.5 percent had been vaccinated with two
doses. Slightly less than two-thirds had received one vaccination.
Most of those who got the chickenpox even though they'd been
vaccinated had a mild case with fewer than 50 lesions on their
bodies. The study also found that hospitalization rates dropped
During 2007 to 2010, just 12 chickenpox outbreaks occurred
within the California site compared with 47 outbreaks during 2003
to 2006, and 236 outbreaks during 1995 to 1998, according to the
Civen said all of these declines can be attributed to the
additional dose of vaccine. "This is solely about getting that
second dose," she noted.
"The varicella vaccine is very effective and safe. It helps those who get the vaccine and others who can't get the vaccine, but are highly susceptible to infection, such as immunocompromised adults," she said.
An expert not involved with the study found its results
"I think the data is pretty clear that the second dose is having a dramatic effect," said Dr. Thomas Murray, a pediatric infectious disease specialist and associate professor of medical sciences at Quinnipiac University's Frank H. Netter MD School of Medicine in North Haven, Conn.
"The second dose in the varicella vaccine program is very effective in reducing varicella in the general population," he said.
The CDC recommends that children under 13 years get two doses of
the chickenpox vaccine: one between the ages of 12 months and 15
months, and the second dose between the ages of 4 and 6 years.
People aged 13 and older who've never had chickenpox or the
vaccine should get two doses, at least 28 days apart, the CDC
Learn more about the chickenpox vaccine from the
U.S. Centers for Disease Control and
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