Updated: Septiembre 29, 2004
Hepatitis B virus (HBV) infection causes both an acute infection and a long-lasting (or chronic) infection. More than half of the people infected with the virus show no signs or symptoms at the time of infection, although they may become chronically infected, developing liver disease or liver cancer later in life. Worldwide, over 350 million people have chronic HBV infection, and approximately 1 million HBV infected people die each year.
Hepatitis B vaccine has proven to both very safe and effective at preventing infection with HBV. Universal immunization of newborn infants, children, adolescents, and high-risk adults is recommended in over 100 countries, including the United States, for protection from serious diseases of the liver, including the prevention of liver cancer. An example of the impact of a HBV immunization program on reducing hepatitis B virus transmission was the experience reported from British Columbia, Canada.1
Although scientific data show that HBV vaccine is very safe,2 anecdotes (personal stories about individual sick persons) have caused some to hypothesize that HBV vaccine might be associated with an increased risk of demyelinating neurological disorders, such as multiple sclerosis (MS). Indeed, such concerns about a possible association of HBV vaccine with MS onset shortly thereafter caused a change in the French HBV immunization policies in 1996.
Concerns about possible causes of disorders like MS following immunization are understandable because of the burden of these diseases on people, their families, and to society. The benefits of HBV vaccine are scientifically well established but occur many years after immunization (prevention of liver failure and liver cancer) and are not fully recognized by many. As a consequence, it is difficult for some to understand the balance between serious but theoretical risks and very real but unappreciated benefits.
How could HBV vaccine cause MS? While hepatitis B virus infection causes liver disease, MS is a disease that affects the central nervous system (CNS, which includes the brain, spinal cord and optic nerves). Although the causes of MS are unknown, it is believed that MS is an autoimmune disease—which means the body’s immune system attacks its own tissues. This concept suggests that somehow HBV vaccine could affect the immune system causing it to attack a fatty tissue called myelin that surrounds and protects the nerve fibers of the CNS, and which helps nerve fibers conduct electrical impulses.3
In 2002, the Institute of Medicine Immunization Safety Review Committee (IOM) reviewed the evidence regarding the hypothesis that the hepatitis B vaccine causes demyelinating disorders.4 The Committee found that evidence for possible mechanisms by which HBV vaccine could cause these diseases was weak. The Committee also concluded that the many published studies provide sufficient evidence to conclude that “the epidemiologic evidence favors rejection of a causal relationship between the hepatitis B vaccine in adults and multiple sclerosis”. However, because of an insufficient number of studies, it was not possible to accept or reject a causal relationship between the HBV vaccine and demyelinating conditions except MS.
Many scientific studies have found no association between receipt of HBV vaccine and subsequent MS.567891011 Also, according to the Immunization Panel of the Multiple Sclerosis Council for Clinical Practice Guidelines, people with an existing diagnosis of MS may be safely immunized with HBV vaccine,12 However, it remains important to consider and re-consider possible serious vaccine adverse effects. For example, there was a recent study that suggested that HBV vaccine could have increased the risk of developing MS among a small proportion of the adults who subsequently developed MS.13
However, because of methodological problems and the fact that this study is in contrast to many other studies, most consider that the findings do not provide convincing evidence of an association.
HBV vaccine has been very successful in decreasing the incidence of hepatitis B over the past decade and has a proven safety record after the administration of millions of doses worldwide. The overwhelming body of evidence continues to favor the rejection of a causal relationship between the HBV vaccine and MS. Data do not justify discontinuation or modification of the HBV immunization program.