By Charles John Palenik
In 1982, implementation of the first vaccine against hepatitis B virus (HBV) began in the United States. When properly applied, the vaccine readily prevents acute HBV disease. Without a primary infection, chronicity cannot occur. Therefore, vaccination eliminates serious sequelae such as hepatitis D infection, cirrhosis, hepatocellular carcinoma and premature death, and is the first immunization against a form of cancer.
Prior to 1982, an estimated 200,000 to 300,000 people in the United States were infected each year. This included approximately 20,000 children. Chronic infections are more likely to occur (in 30 to 90 percent of cases) among children under the age of five. In contrast, chronic infections develop in only 2 to 10 percent of people infected after the age of five.
Since 1982, an estimated 40 million infants and children and 30 million adults have received the HBV vaccine. Because of vaccination and because of behavioral changes among people at increased risk for HIV/AIDS, the number of people infected with HBV in 2001 declined to 79,000.
Occupational risks
Frequent exposure to patient blood and body fluids places dental hygienists at increased risk for HBV infection. Before 1982, no practical method of preventing infection existed. Post-exposure prophylaxis involved the application of hepatitis B immune globulin (HBIG). Few dental practitioners routinely wore gloves and less attention was given to needlestick accidents.
The prevalence of HBV serologic markers among dentists in the pre-vaccination era was thought to be about 15 percent with an annual attack rate of 2 percent. At that time, approximately 5 percent of the general American population was seropositive due to current or past HBV infections. Twenty years ago, dental hygienists had prevalence rates slightly higher than those of dentists. Somewhat lower attack rates (about 13 percent) were noted among dental assistants. Prevalence was highest among oral surgeons — over 30 percent with a 5 percent annual attack rate.
A concern
Recently, a meta-analysis of more than 20 publications reviewed the possible association of age with response to HBV vaccination. Meta-analysis is a set of statistical procedures designed to accumulate experimental and correlational results across independent studies that address a related set of research questions.
The study detected a link between increased age and inadequate immune response to HBV vaccination. A risk was observed even when "older individuals" were defined as being as young as 30. It is known that both cellular and humoral immune responses decrease as a person ages. There was no evidence that either of the two vaccines was more immunogenic in older persons. The routine use of a fourth injection or booster shots did not decrease the risk for non-responders among older individuals.
These results are clinically important and could affect HBV vaccination policies. An inadequate response may now include individuals young enough to be at-risk for long-term complications of chronic HBV infection, such as cirrhosis and hepatocellular carcinoma and could affect persons of childbearing age.
If non-responders are given a single additional injection, 15 to 30 percent will seroconvert to protective levels. Repeating the entire series results in an adequate response in 30 to 50 percent of cases. Failure to seroconvert after two complete vaccination series may indicate the presence of a chronic HBV infection. Non-responders, when exposed, will require HBIG injections.
Ideally, vaccine recipients should be serologically screened within two to three months after completing their immunization series. However, not all vaccine recipients have been screened or screened promptly. Antibody levels of persons vaccinated more than five years ago may not be detectable. Such persons should consult with a gastroenterologist.
Duration of protection is not known. However, properly immunized people are known to be protected by memory immune cells for periods of at least 15 years. Exposure to HBV produces an anamnestic response, which prevents clinically significant HBV infection. Booster doses of vaccine are not routinely recommended.
The leading source of safety and health information for dental practices, the Organization for Safety and Asepsis Procedures (OSAP), offers a wealth of compliance information via newsletters, training systems and a Web site. Visit the OSAP Web site — www.osap.org — for links to more than 50 OSHA-related topics.
Two HBV vaccines are currently licensed for use in the United States — Recombivax HB (Merck) and Engerix-B (GlaxoSmithKline). Both employ recombinant technology and contain hepatitis B virus surface antigen produced by baker's yeast, Saccharomyces cerevisiae. Live or attenuated virus is not present in the vaccines. There is also a combined hepatitis A (HAV) and HBV vaccine called Twinrix. It contains the antigenic components of Havrix (HAV) and Engerix-B.
For adults, vaccination usually involves a series of three injections. The first two are given four weeks apart, while the third is administered four to six months after the first. The vaccines are interchangeable and are generally well tolerated with pain at the site of injection being the most common adverse reaction.
If properly administered, the vaccines are 90 to 95 percent effective in preventing HBV infection and clinical hepatitis among susceptible, healthy children and younger adults. Lower levels of seroconversion can be found among immunosuppressed individuals, males, or those who are overweight or smoke. Some people appear to be genetically predisposed to inadequate antibody development.
Charles John Palenik, MS, PhD, is an assistant director of Infection Control Research and Services at the Indiana University School of Dentistry. Dr. Palenik has authored numerous articles, book chapters and monographs, and is the co-author of the popular Infection Control and Management of Hazardous Materials for the Dental Team. He serves on the Executive Board of OSAP, dentistry's resource for infection control and safety.Questions about this article or any infection control issue may be directed to [email protected].
