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Vaccination Tames Hepatitis A Infection

U.S., Israeli studies find inoculating children lowers incidence in entire population

TUESDAY, July 12, 2005 (HealthDay News) -- Vaccinating children, especially young ones, can dramatically decrease the incidence of hepatitis A infections.

Two new studies -- one from Israel, the other from the United States -- found that childhood vaccination programs could reduce the incidence of disease by as much as 98 percent.

"Hepatitis A disease can be rapidly controlled by vaccination," said Dr. Ron Dagan, one of the Israeli study's authors and director of the pediatric infectious disease unit at Soroka Medical Center at Ben Gurion University in Beer-Sheva, Israel.

"By vaccinating kids, we've dropped the incidence from 10 per 100,000 to two per 100,000, which is a remarkable achievement," said Annemarie Wasley, an author of the U.S. study and an epidemiologist in the division of viral hepatitis at the CDC.

Results of both studies appear in the July 13 issue of the Journal of the American Medical Association.

Hepatitis A is a viral infection that generally causes flu-like symptoms, but can also cause the liver disease jaundice. The infection usually clears up without treatment in three months or less. Unlike other forms of hepatitis, such as hepatitis B or hepatitis C, hepatitis A does not turn into a chronic illness. It is transmitted through contaminated food or water, or from the stool of someone who currently has the infection, according to the National Institutes of Health.

An estimated 270,000 Americans contracted hepatitis A annually during the 1980s and 1990s, according to background information in Wasley's study. In 1995, effective vaccines for the disease became available, and the CDC initially recommended vaccination only for people in high-risk groups, such as drug users, gay men and people traveling to areas where hepatitis A outbreaks are common. In 1999, those recommendations were expanded to include children living in U.S. states with high rates of infection.

Wasley's study was designed to assess the impact of that change. She and her colleagues compared surveillance information from 2003 to data gathered before an effective vaccine was available in the early to mid-1990s.

They found that across the United States, the overall rate of hepatitis A declined 76 percent by 2003. In children aged 2 to 18, that decline was 87 percent, while adults saw an overall decline of 69 percent.

In states with previously high levels of infection, and higher vaccination rates in 2003, the rate plummeted 88 percent, according to the study.

In the Israeli study, researchers compared data on hepatitis A incidence before vaccination with data gathered after Israel began a universal vaccination program for toddlers in 1999.

"Israel was considered until 1999 to be a country with endemic hepatitis A disease, with disease rates exceeding that of the U.S. several-fold, approximately five to six times," Dagan said.

"Shortly after introduction of the vaccine, the disease rates started to drop and within less than three years, a dramatic decrease of greater than 95 percent was seen in the overall disease rate, which has been sustained for three successive years now. The rate is now lower than the mean disease rate in the U.S.," Dagan added.

In both studies, those vaccinated weren't the only ones who benefited. Young children infected with the disease often don't show symptoms but can still infect others, making them a common source of infection, according to the studies.

"Because the motor of such an epidemic was targeted [with vaccination], other cohorts are no longer exposed to the virus. Targeting one cohort appears then to have a population effect, called herd immunity," explained Dr. Pierre Van Damme, author of an accompanying editorial in the same issue of the journal and a professor of social medicine at the University of Antwerp, in Belgium.

All three experts pointed out that there is a natural five- to 10-year cycle of hepatitis A infections, and it's possible that some of the decline seen was simply part of the natural cycle. However, they believe the vaccination programs are responsible for the bulk of the decline.

Besides vaccination, Van Damme said that simple measures, such as washing your hands before eating and after going to the bathroom, can also help prevent the spread of hepatitis A.

More information

To learn more about hepatitis A, visit the CDC.

SOURCES: Annmarie Wasley, Sc.D., epidemiologist, division of viral hepatitis, U.S. Centers for Disease Control and Prevention, Atlanta; Ron Dagan, M.D., professor, pediatrics and infectious disease, and director, pediatric infectious disease unit, Soroka Medical Center and the Faculty of Health Sciences at Ben Gurion University, Beer-Sheva, Israel; Pierre Van Damme, M.D., professor, social medicine, University of Antwerp, and director, Centre for the Evaluation of Vaccination, World Health Organization Collaborating Centre for the Prevention and Control of Viral Hepatitis, Wilrijk, Belgium; July 13, 2005, Journal of the American Medical Association
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