"Vaccine reduces hepatitis A"
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|Fri, 08-08-2003 - 1:23am|
Vaccination programs effectively reduce hepatitis A incidence
Vaccine programs are shifting disease incidence to high-risk groups like injection drug users and men who have sex with men.
by Colleen Zacharyczuk
SAN FRANCISCO — Hepatitis A vaccination programs directed at children have been effective at reducing disease rates, however, challenges remain with the main challenge being to sustain ongoing vaccination efforts in the face of falling disease rates.
“Ultimately I think you can think about eliminating transmission of this virus,” said Harold Margolis, MD, director of the division of viral hepatitis at the CDC, speaking at the 5th Annual Infectious Diseases in Children Symposium West.
Margolis said the difficult issue with hepatitis A (HAV) is that it is a stable virus and, as such, is easily transmissible.
“It’s got a long incubation period, an average of one month from exposure, and expression of the disease is age dependent, 85% of kids infected are asymptomatic,” Margolis said. On a positive note, however, the case- fatality rate is low, only about three per 1,000 cases.
Approximately 10% of people with HAV will relapse, Margolis said, at which point, they are infective again.
Exposure is usually the fecal-oral route, through personal contacts, usually within the household, Margolis said. An infected individual can become clinically ill with jaundice. Relapsing hepatitis A, acute liver failure, autoimmune hepatitis, and extrahepatic manifestations can be associated with the disease.
Before the hepatitis A (Hep A) vaccine was licensed, certain trends in infection were noted. The number of people infected with HAV was consistently much higher in the western part of the country. The reason for this, according to Margolis, was that areas with high populations of Native Americans and Hispanics had higher rates of hepatitis A.
Trends were also noted in certain high-risk groups — with higher incidences of infection in men who have sex with men (MSM) and injection drug users (IDUs).
“Seroprevalence is always higher in injection drug users, and they also found that non-injection drug users also get hepatitis A,” he said, “that is because there is a lot of handling during drug preparation activities, and they also don’t live in the most hygienic of settings.”
Another setting where infection is common, he said, is in travelers. “Children are travelers and we know that travel accounts for about 10% of cases,” he said. “Children represent about a third of those cases, and Mexico is the most frequent destination for children with travel-related hepatitis A. Especially at risk are U.S. born children returning to the home country of their parents.”
The epidemiology and consequences of HAV infection prompted the Advisory Committee on Immunization Practices (ACIP), in 1996, to recommend targeted vaccination for adults and children in groups at risk of infection (eg, travelers, MSM, IDUs), and the consequences of infection (people with chronic liver disease), and routine vaccination of children in communities with high rates of HAV. The immunization strategy for hepatitis A is based on the vaccination strategy used to control polio. Initially there was catch-up vaccination to raise immunity in the population, followed by routine immunization of young children and infants to eliminate transmission, Margolis said.
In 1999, the ACIP expanded its recommendations for routine childhood vaccination to those states where the rate of disease was greater than 20 cases per 100,000 during 1987-1997; this rate being twice the national average over this 10 year period.
As might have been expected, Margolis said, this strategy has had a clear impact on disease rates, particularly in certain groups, for instance, Native Americans. In the early 1990s, rates of hepatitis A in the Native American population were six to eight times higher than the national average, however, following widespread vaccination an unprecedented drop in rates was documented.
In 2001, for the first time, the hepatitis A rate of Native Americans dropped below that of the national average.
In addition to the dramatic decline in HAV among American Indians/ Alaska Natives, there has been a similar decline in overall hepatitis A disease rates — current disease incidence is the lowest ever recorded. Another effect of the current recommendations is that because most immunization has occurred among children, their incidence of disease, which has always been several times higher than the incidence in adults, has now dropped to almost the same rate as seen in adults.
So far, those recommendations are having an impact, Margolis said.
“There was an 83% decline noted in those states where vaccination was universally recommended,” he said. “So we know vaccination has reduced rates of infection to historic lows, and it’s shifting disease incidence to adults in high risk groups like men who have sex with men and injection drug users.”
Two hepatitis A vaccines are licensed for use in children beginning at 2 years of age and both have a 2-dose schedule. These are Havrix (GlaxoSmithKline), which can be used at the pediatric dose until age 17, and Vaqta (Merck), which can be used at the pediatric dose until age 18.
Margolis also said that pediatricians in all parts of the United States should continue to identify children in groups at increased risk of infection or adverse consequences from hepatitis A — travelers, young men who have sex with men, drug users, and those with chronic liver disease – so that they may be given the vaccine.
For more information:
Margolis H. Prevention and control of hepatitis A. Presented at the Fifth Annual Infectious Diseases in Children West. May 31-June 2, 2003. San Francisco.
Dr. Margolis has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.