Sep. 8, 2004 ANN ARBOR, Mich. -- The chicken pox vaccine has saved America hundreds of millions of dollars since its introduction in 1995 by preventing the kinds of severe cases that used to send children, teens and adults to the hospital, a new study finds. In fact, it's even more effective -- and cost-effective -- than originally predicted at preventing hospitalizations and hospital costs.
And the widespread immunity to the disease that has resulted from vaccination of most children even appears to be protecting people who haven't had the shot, the researchers say. Fewer infections among kids means less exposure for teens and adults who haven't had the disease or the vaccine -- and who are most likely to need hospital treatment for symptoms and complications if they get the disease.
In a paper in the September issue of the journal Pediatrics, a team from the University of Michigan C.S. Mott Children's Hospital gives the first data ever to report a national decrease in chicken pox-related hospitalization occurring simultaneously with the rise in immunization rates for the disease.
"The results show an annual savings of $100 million since the varicella, or chicken pox, vaccine was introduced, just in the cost of hospital care for people with severe cases. That's greater than the savings predicted in the vaccine's pre-approval analysis," says lead author and U-M pediatrician Matthew M. Davis, M.D., M.A.P.P. "The hospital bill savings were considerable for Medicaid and private insurers, and ultimately for the taxpayers, employers and employees who pay for that coverage."
The savings don't include other chicken pox costs, such as doctor visits, prescription drugs, over-the-counter remedies or lost work time for parents or adult patients -- all of which are also expected to be reduced as a result of the chicken pox vaccine.
But the yearly hospital cost savings alone are enough to pay for a large portion of the total cost of vaccinating all American kids against chicken pox, Davis says.
The study shows that the national rate of hospital discharges for chicken pox and related complications dropped 74 percent in the first six years after the vaccine first went on the market. Before the vaccine, there was one chicken pox-related hospitalization each year for every 20,000 Americans. By 2001, when 76 percent of toddlers had been vaccinated, the rate was 0.26 hospitalizations per 20,000 people.
The Centers for Disease Control and Prevention estimates that before the vaccine, there were 4 million cases of chicken pox nationwide each year, resulting in 11,000 hospitalizations and 100 deaths. Most cases were treated at home.
After the vaccine's introduction, the new study shows, the biggest drop in hospitalization rates was among young children, for whom the vaccine has been recommended since 1995 and is now required for school or day care enrollment in most states.
But teens and adults also had a decline in hospital costs, probably due to an effect called "herd immunity" that keeps the virus from spreading among unvaccinated, previously uninfected people.
Of course, adults and teens who have not yet had chicken pox or the varicella vaccine should consider protecting themselves against possible infection by getting vaccinated, says Davis, an assistant professor of pediatrics and general internal medicine at the U-M Medical School and assistant professor of public policy at the U-M's Gerald R. Ford School of Public Policy.
"This is especially important for anyone who works around children," Davis explains. "And women of childbearing age, because they can't get vaccinated during pregnancy. With chicken pox there's tremendous danger to the fetus during development, and to babies born to infected mothers." For people over the age of 12, vaccination involves two shots a month apart, and costs about $125.
And, he adds, the "herd immunity" effect doesn't mean parents can skip getting a child vaccinated. "If anything, we need to ensure the highest possible vaccination rates among children, to get the most benefit for everyone," he says. "These data show we can't afford to slow down."
Children aged 1 to 12 years who have never had chicken pox need one shot, according to CDC recommendations. It's often covered by private insurance and Medicaid or, if a child is uninsured, can be given by a clinic that gets vaccine from the CDC's Vaccines for Children program. Recently, other research reports have found that while vaccinated children can still get the chicken pox, they're most likely to get a very mild case that is far less likely to need hospitalization.
The study was based on data from the Agency for Healthcare Research and Quality and funded by the U-M Health System. The team correlated national vaccination rates from the CDC's National Immunization Survey with hospital discharge, diagnostic coding, hospital cost and insurance data from AHRQ's Nationwide Inpatient Sample, part of the Healthcare Cost and Utilization Project.
The hospital costs included charges for treating pneumonia or encephalitis in people with chicken pox; for hospital treatment during a chicken pox infection of people with AIDS, cancer, an organ transplant or immune disorders; and for other known complications of severe chicken pox, such as skin infections, in hospital patients who had a confirmed diagnosis of the disease.
After calculating hospital discharge rates in various populations using federal Census data, and adjusting all costs into 2001 dollars, the researchers could see the trends they report in the paper. Their graph that maps overall varicella vaccination rates against hospital discharge rates for 1993 to 2001 shows two strikingly different curves: one heading steadily downward for hospitalization, and one going sharply up for vaccination, starting in 1996, the first full year of the vaccine's availability.
When the hospitalization curve is broken down into ages 0 to 4, ages 5 to 9, ages 10 to 19 and age 20 or older, the sharpest decline is among 0 to 4 year olds, the first group targeted for vaccination. But all other groups declined too. "We're getting to kids before their peak risk years," says Davis.
Meanwhile, a graph showing chicken pox-related hospital costs in constant 2001 dollars shows costs hovering near $160 million from 1993 to 1997, and then four years of marked decline to about $60 million in 2001. Medicaid reaped major savings, going from $75 million in costs in 1993 to less than $20 million in 2001, the most dramatic drop for any form of health insurance.
"This underscores the importance of national vaccination for the most vulnerable populations, and shows that federal and state efforts to achieve this vaccination are working," says Davis.
Looking forward, Davis and his colleagues will continue to assess the national chicken pox hospitalization patterns for 2002 and beyond, to see what has happened as vaccination rates have risen above the 76 percent seen in 2001.
"This first phase of national vaccination against chicken pox appears to have substantially reduced the burden of severe illness in all age groups," he says. "What remains to be seen is what the pattern will be as we get closer to having all children vaccinated, and how long the protective effect of the vaccine and the herd immunity lasts."
In addition to Davis, the paper's authors are Mitesh S. Patel, B.S., and Acham Gebremariam, M.S., both of the U-M Department of Pediatrics. All the authors are part of the U-M's Child Health Evaluation and Research Unit, which has several grants to study vaccine-related issues. None of the authors has any financial connection to the varicella vaccine's manufacturer.
Reference: Pediatrics, September, 2004, 114 (3)
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