The Hepatitis B Vaccine
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Hepatitis B is a nasty virus because of its potential to turn into chronic, progressive liver disease. With the possibility of leading to severe liver damage, such as cirrhosis and hepatocellular carcinoma, monumental efforts have been launched to prevent infection with Hepatitis B. Thankfully, the Hepatitis B vaccine is over 95 percent effective in protecting infection in those who have never contracted the virus before. Part of the routine vaccination requirements for infants since the early 1980s, nearly every baby in the U.S. receives this protection. However, there is some evidence that the immunity provided by the Hepatitis B vaccine may begin to wear off with time.
Consisting of a series of three injections, the Hepatitis B vaccine is required by most U.S. states for children prior to beginning daycare or public school. Over the past decade, the mandated vaccination of American children has been directly linked to the dramatic reduction of new Hepatitis B infections.
Immune Memory
While there is little data regarding the duration of protection provided by the Hepatitis B vaccination, scientists believe the immune system’s memory is at the heart of vaccination longevity. A successful primary immune response results in the production of immune system B-cells that have high affinities for the pathogen causing the response. Typically these B-cells are short-lived, making us believe that elimination of the pathogen also ends in B-cell death. If this were always the case, another exposure to the same pathogen would have to begin the propagation of specialized B-cells all over again. However, the immune system can avoid this repetitive process by retaining a memory of the pathogen’s information in the adapted B-cells.
Because of immune memory, the primary response to new pathogens is typically slow, while memory of previously encountered pathogens allows the immune system to mount a much faster attack. The presence of immune memory can be evaluated indirectly by measuring the immune response to a booster dose of the vaccine. Known as an anamnestic response, immune memory is determined when a renewed rapid production of antibodies on the second (or subsequent) encounter occurs with the same antigen.
Taiwan Leads the Way
Twenty years ago, Taiwan was the first country to successfully implement a universal Hepatitis B vaccination program for infants. As evaluated by scientists, two Taiwanese studies investigated Hepatitis B immune memory and demonstrated that the vaccine may be less effective for certain individuals.
Study 1 – As published in the April 2007 issue of Gastroenterology, researchers from Taiwan evaluated the long-term effectiveness of the Hepatitis B vaccine. After assessing nearly 19,000 study participants, the authors concluded the following:
- For most people, universal Hepatitis B vaccination provides immune memory, and therefore long-term protection for up to 20 years.
- For those receiving vaccination as infants, universal Hepatitis B booster is not necessary before adulthood.
- Maternal transmission of Hepatitis B is the primary reason for vaccine failure.
- In the future, high-risk infants may require amended vaccination programs.
Study 2 – As reported in the June 2007 issue of Journal of Hepatology, Taiwanese researchers evaluated the booster response of adolescents without Hepatitis B who had received infant vaccination. The researchers found that the following factors significantly increased the risk of non-response to booster vaccination:
- Cigarette smoking
- Betel-quid chewing
- Alcohol consumption
- Malay-Polynesian ethnicity
The authors concluded that Hepatitis B booster vaccine may be insufficient to provide protection to people of Malay-Polynesian ethnicity or in those with recent cigarette smoking, alcohol consumption and/or betel-quid chewing.
Alaska Study
In a study published in the July 16, 2007 online edition of Pediatrics, researchers enrolled 378 healthy participants recruited at the Alaska Native Medical Center between October 2001 and January 2004. All subjects were born to mothers without the Hepatitis B virus and received their first dose of the Hepatitis B vaccine within seven days after birth. By evaluating the immune memory of participants, study investigators found that differences in immunity existed.
According to the Alaskan researchers’ findings, only 60 percent of 14 year-olds had an anamnestic response to a Hepatitis B vaccine booster dose, compared with 97 percent of five year-olds. The authors concluded, “Although most participants responded to a booster dose of Hepatitis B vaccine, the significance of the increased proportion of non-responders among older adolescents might indicate waning immune memory.”
Most physicians do not recommend a booster dose of the Hepatitis B vaccine for a person who has received the infant vaccination until adulthood. However, some of the recent evidence suggests we take a closer look at how long the Hepatitis B vaccine immune memory actually lasts. Factors such as ethnicity, people with compromised immunity, cigarette smoking, alcohol consumption or maternal transmission, are all being looked at as possible precursors to fading Hepatitis B immunity. Until more information is gathered, experts agree that further studies are needed before booster doses of Hepatitis B vaccine intended to maintain long-term immunity are recommended.
References:
http://medicine.com.my, Do You Need a Booster for Hepatitis B?, Palmdoc, Malaysian Medical Resources, May 2007.
Samandari, MD, PhD, Taraz, et al., Differences in Response to a Hepatitis B Vaccine Booster Dose Among Alaskan Children and Adolescents Vaccinated During Infancy, Pediatrics, August 2007.
www.cdc.gov, Vaccines & Immunizations, Centers for Disease Control and Prevention, 2007.
www.cs.unm.edu, Immune Memory, Steven A. Hofmeyr, University of New Mexico, 2007.
www.hivandhepatitis.com, Differences in Response to a Hepatitis B Vaccine Booster among Children and Adolescents Vaccinated during Infancy, hivandhepatitis.com, August 2007.
www.hivandhepatitis.com, Hepatitis B Vaccination Provides Long-term Protection, but All Do Not Respond Equally, Liz Highleyman, hivandhepatitis.com, 2007.
www.medpagetoday.com, Hepatitis B Vaccine Protection May Not Be Long-Lasting, Peggy Peck, August 2007.
www.thefreedictionary.com, anamnestic response, Farlex, Inc., 2007.
YH Ni, LM Huang, MH Chang, et al., Two Decades of Universal Hepatitis B Vaccination in Taiwan: Impact and Implication for Future Strategies, Gastroenterology, April 2007.
