In the United States, Hepatitis A is one of the most commonly reported diseases that can be prevented by a vaccine. The CDC estimates that each year in the U.S. 180,000 people contract hepatitis A, half of whom develop no symptoms and therefore spread it unknowingly. Although an effective vaccine has been available here since 1995, about 100 people still die each year from liver failure caused by hepatitis A.

In North America cases of hepatitis A have peaked in 1954, 1961, and in the early 1970s. Smaller peaks were noted in the late 1980s and mid-1990s. As sanitary conditions improve, these peaks every 5 to 10 years have involved many fewer people.

Like polio, hepatitis A is most common in children, probably because it is spread in the stool. Also like polio, hepatitis A tends to cause more severe disease in adults. Among preschool children, only about 30 percent get symptoms, but more than 70 percent of older children and adults get symptoms from hepatitis A infection. Three out of 1,000 persons who contract hepatitis A die from it, but 18 out of 1,000 people die in the 50 and older age group.

Hepatitis A vaccine has not been very controversial up to now because most of the people receiving it have been adults who suspected they would be exposed to hepatitis A, for example, during travel to a developing country. In 1999, CDC recommended the vaccine for all children 2 to 18 years old in states, counties, or communities where hepatitis A virus infections are common (mainly in the western states).

Parents may be concerned about giving the vaccine to their child since hepatitis A is rarely life threatening and not a significant risk until later in life. The purpose of CDC's recommendation is both to protect individuals and to stop the spread of the hepatitis A virus. Like many germs that are spread in stool, children spread the hepatitis A virus to other children, but studies in the U.S. have shown that children also often spread the disease to adults who are not already immune.

A second concern is vaccine safety. Before licensing, hepatitis A vaccines were carefully evaluated for safety. Since the vaccine was licensed, it has been administered to millions more. Now that the vaccine is recommended as a routine childhood vaccine in some areas of the country, many times the number of children who received it previously will receive it between the years 2000 and 2005. Will the vaccination of millions of children reveal previously unsuspected problems? It is very unlikely, but CDC has identified the evaluation of hepatitis A vaccine safety as an issue that should be addressed in future studies.

Finally, another potential concern is that, like chickenpox, hepatitis A tends to be a more serious disease if one's first exposure comes later in life. Unlike the vaccine against chickenpox, however, the vaccine against hepatitis A is inactivated (not live), so there is less certainty that it will provide lifelong immunity. By giving the vaccine during childhood, are we only postponing the disease until later in life when its danger increases? As of this writing, the longest currently available study is seven years, and it shows that the vaccine is continuing to protect. On the basis of current data, scientists expect the vaccine to work for 20 years or more. CDC is conducting studies to evaluate the long-term protection afforded by hepatitis A vaccine. Just as with chickenpox, children who receive the vaccine in the first decade of the twenty-first century and who live in communities with a high prevalence of hepatitis A will continue to receive boosters through exposure to the live virus out in the community