At present, there is no need for government advisory bodies to review policy that encourages the vaccination of infants, adolescents, and adults at high risk of exposure to the hepatitis B virus, such as health care workers, to protect them against serious liver damage.

"Hepatitis B vaccine policy has been viewed skeptically by some because of concerns about vaccine safety and a perception that the virus itself does not pose a serious risk," said Marie McCormick, chair of the committee that wrote the report, and professor and chair, department of maternal and child health, Harvard School of Public Health, Boston. "However, the committee heard testimony about the seriousness of the disease, especially for young children, and growing evidence of the benefits of the vaccine. Hopefully, our report will ease the concerns of adults who need to be immunized against hepatitis B and are worried about the risk for multiple sclerosis."

In the United States, one out of 20 people will contract the hepatitis B virus through direct contact with the blood or body fluids of an infected person. The younger people are when they become infected, the more likely they will develop the chronic form of the disease.

For example, chronic infection is likely to occur in 90 percent of infected newborns and 6 percent of infected adults. They face serious health consequences and no cure. A quarter of those with chronic hepatitis B will die from cirrhosis or liver cancer, including children who will not reach young adulthood. These chronic carriers can infect others. Sometimes a person with the infection has no symptoms at all, and only a blood test can reveal it.

In 1982, a vaccine for hepatitis B became available in the United States. Looking at people born in 1998, the Centers for Disease Control and Prevention estimated that about 6,800 perinatal infections and 18,700 infections of infants and children up to the age of 9 would have occurred without immunization.

About 12,100 of these children would have developed the chronic form of the disease, and about 3,000 would have eventually died from cirrhosis or liver cancer.

The committee did a comprehensive assessment of evidence pertaining to the theory that the hepatitis B vaccine causes what are known as demyelinating neurological disorders, including multiple sclerosis and Guillain-Barré syndrome.

Myelin surrounds nerve fibers, providing protection like insulation on an electric wire, and contributes to the transmission of signals through the nervous system. When inflammation within the body causes myelin to be damaged or destroyed, nerve fibers can be injured and the transmission of nerve impulses that control bodily functions and mobility can be seriously disrupted.

The hypothesis that vaccines such as hepatitis B could cause these disorders has a theoretical basis, but the existing evidence does not support it, the committee said.

Biological evidence that the hepatitis B vaccine affects the immune and nervous systems in ways that could lead to these diseases is weak,and the epidemiological evidence rejects the notion that the vaccine causes the onset or relapse of multiple sclerosis in adults.

No studies address the risk of MS following hepatitis B immunization in infants or children. In addition, the committee could not completely rule out a causal relationship between the hepatitis B vaccine and all other conditions brought on by damage to the myelin sheath, such as inflammation of the optic nerve and inflammation of the brain and spinal cord.

It recommended continued surveillance of demyelinating diseases -- especially in health care workers and people born since 1991, when routine administration of the vaccine to newborns and infants began -- and more research, as well as better communication to the public about the risks and benefits of the vaccine.

For this review, the committee examined the relationship between hepatitis B vaccine and the more serious demyelinating diseases: of the central nervous system, multiple sclerosis (onset or relapse), acute disseminated encephalomyelitis, optic neuritis, and transverse myelitis; and of the peripheral nervous system, Guillain-Barré syndrome and brachial neuritis.

An extensive collection is available of published, peer-reviewed scientific and medical literature investigating the association of these diseases with the hepatitis B vaccine.

Multiple sclerosis is the most common chronic inflammatory demyelinating disease of the central nervous system. In the United States, about 300,000 individuals have the disease, and women are affected about twice as often as men.

Common initial symptoms include vision and balance problems and fatigue. The cause of MS remains elusive, but susceptibility appears to involve both genetic and environmental factors.

Guillain-Barré syndrome is the most common peripheral demyelinating disease, with one to two cases occurring annually per 100,000 people. It typically develops several days or weeks after an infection, such as a diarrhea or viral upper respiratory illness. It is characterized by temporary but rapidly progressive muscle weakness. Most patients will improve gradually and return to normal function within six to nine months, but some experience relapses or residual neurological problems.

This study is the fourth in a series of eight on vaccine safety sponsored by the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases.

The Institute of Medicine is a private, nonprofit institution that provides health policy advice under a congressional charter granted to the National Academy of Sciences.

[Contact: Bill Kearney]

03-Jun-2002