USA--Rates of new hepatitis Aand B infections have declined to the lowest levels ever recorded, largely because of routine childhood vaccination, according to new data from the Centers for Disease Control and Prevention. But the news is not so good about hepatitis C, for which there is no vaccine. In 2006, the latest year for which data is available, 3.2 million Americans were chronically infected with hepatitis C, which can cause liver cancerand is the most common reason for liver transplantation. While the number of new infections was small, it increased slightly each year since 2003.

Hepatitis A, B and C are caused by three different viruses, often abbreviated HAV, HBV and HCV. Hepatitis A is usually transmitted by contact with infected feces. Before the vaccine came along in 1996, outbreaks occurred roughly every 10 years, which is why there are two humps in the first graph below.

Hepatitis B spreads through blood and body fluids, from mother to infant during delivery, and sometimes by long-term contact with an infected person. Rates are higher for men than for women because two of the groups most at risk are injection drug users (most of whom are men) and men who have sex with men.

HCV is passed through blood or body fluids.

“The trends in A and B reflect the power of vaccinationsto prevent disease to the point where we can talk about eliminating them,” said Dr. John W. Ward, director for viral hepatitis at the C.D.C. “Hep C is common in the U.S., and more effective interventions are needed.”