Definitions

anti-hbs

Hepatitis B vaccine

Hepatitis B vaccine is a vaccine developed for the prevention of hepatitis B virus infection. The vaccine contains one of the viral envelope proteins, hepatitis B surface antigen (HBsAg). After a course of three (3) vaccine injections, an immune system antibody to HBsAg is established in the bloodstream. The antibody is known as anti-HBsAg. This antibody and immune system memory then provide immunity to hepatitis B infection.

History

The vaccine was originally prepared from plasma obtained from patients who had long-standing hepatitis B infections. However, vaccines currently used in the United States are made using recombinant DNA technology. The two types of vaccines are considered equally effective. In the United States, two of the newer recombinant vaccines are Engerix-B (made by GlaxoSmithKline), and Recombivax HB (made by Merck). The recombinant vaccines consist of proteins produced in modified yeast cultures. Unlike plasma-derived vaccines, these recombinant vaccines are not produced using human cell lines or human tissue material.

Infection with hepatitis B may lead to hepatocellular carcinoma, a type of liver cancer. Therefore, the hepatitis-B vaccines are cancer-preventing vaccines. According to the Centers for Disease Control and Prevention (CDC), the hepatitis B vaccine was the first anti-cancer vaccine.

Recommended populations

Babies born to mothers with active hepatitis B infections are recommended to receive treatment reducing the risk of mother-to-child transmission of the hepatitis B infection. As soon as possible and within 48 hours of birth, newborns are vaccinated with hepatitis B surface antigen (HBsAg) and injected with hepatitis B immune globulin (HBIG).

Many countries now routinely vaccinate infants against hepatitis B. In countries with high rates of hepatitis B infection, vaccination of newborns has not only reduced the risk of infection, but has also led to marked reduction in liver cancer. This was reported in Taiwan where the implementation of a nationwide hepatitis B vaccination program in 1984 was associated with a decline in the incidence of childhood hepatocellular carcinoma.

In many areas, vaccination against hepatitis B is also required for all health-care and laboratory staff. Some college campus housing units now require proof of vaccination as a prerequisite.

An Australian couple in August 2008 went on the run after the New South Wales Supreme Court extended an order forcing them to immunise their newborn against the disease. DOCS (Department of Community Services) took out the order, as doctors say the five-day-old baby is at a high risk of contracting the illness as his mother has the disease. The parents believe (see Vaccine controversy) that aluminium in the vaccine would cause the baby more harm than the disease itself.

Response to vaccination

Following the primary course of 3 vaccinations, a blood test may be taken after an interval of 1–4 months to establish if there has been an adequate response, which is defined as an anti-hepatitis B surface antigen (anti-Hbs) antibody level above 100 mIU/ml. Such a full response occurs in about 85-90% of individuals.

An antibody level between 10 and 100 mIU/ml is considered a poor response, and these people should receive a single booster vaccination at this time, but do not need further retesting.

People who fail to respond (anti-Hbs antibody level below 10 mIU/ml) should be tested to exclude current or past Hepatitis B infection, and given a repeat course of 3 vaccinations, followed by further retesting 1–4 months after the second course. Those who still do not respond to a second course of vaccination may respond to a high dose of vaccine or to intradermal administration. Those who still fail to respond will require hepatitis B immunoglobulin (HBIG) if later exposed to the hepatitis B virus.

Poor responses are mostly associated with being over the age of 40 years, obesity and smoking, and also in alcoholics, especially if with advanced liver disease. Patients who are immunosuppressed or on renal dialysis may respond less well and require larger or more frequent doses of vaccine. At least one study suggests that hepatitis B vaccination is less effective in patients with HIV.

Duration of protection

Although initially it was thought that the hepatitis B vaccine did not provide indefinite protection, this is no longer considered the case. Previous reports had suggested vaccination would provide effective cover of between five and seven years, but subsequently it has been appreciated that long-term immunity derives from immunological memory which outlasts the loss of antibody levels and hence subsequent testing and administration of booster doses is not required in successfully vaccinated immunocompetent individuals. Hence with the passage of time and longer experience, protection has been shown for at least 25 years in those who showed an adequate initial response to the primary course of vaccinations, and UK guidelines now suggest that for initial responders who require ongoing protection, such as for healthcare workers, only a single booster is advocated at 5 years.

See also

References

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