Significant numbers of people who receive the vaccine against the hepatitis B virus (HBV) as infants will already be vulnerable to HBV infection by the time they reach adolescence, according to a study conducted by researchers from Mackay Medical College in New Taipei City, Taiwan and published in the journal Hepatology.
“While infantile HBV vaccination is highly effective, it is not 100 percent and our study examines the long-term success of the HBV vaccine in a high-risk population,” lead author Li-Yu Wang said
Public health officials consider HBV a major global health concern, with approximately two billion people infected worldwide plus another 360 million people considered chronic carriers of the hepatitis B surface antigen (HBsAg).
The presence of HBsAg in the body is considered a marker of active HBV infection.
“Chronic HBV is a major health burden that leads to cirrhosis, liver cancer … and liver failure,” Wang said.
The United States has some of the lowest HBV infection levels in the world, with only about 0.5 percent of the population infected. Taiwan, in contrast, has an infection rate of approximately 95 percent, with about 20 percent of the population also classified as HBsAg carriers. As a result, Taiwan became the first country to initiate universal HBV vaccination in the 1980s. Prior studies indicate that the vaccination program was indeed successful in reducing infection and carrier rates among Taiwanese children, as well as reducing cases of severe hepatitis in infants and childhood liver cancer.
Reinfection still possible
The researchers tested 8,733 high school students who had been born between July 1987 and July 1991 for the presence of HBsAg and its antibodies, and also examined their vaccination records. The participants had a mean age of 16 and were all students at schools in Hualien County in eastern Taiwan. 53 percent of study participants were male.
The researchers found that although all the students had been vaccinated against HBV as children, two percent of them tested positive for HBsAg, indicating infection, while 48 percent – nearly half – tested positive for antibodies to HBsAg, indicating an immune reaction to HBV exposure.
HBV is transmitted sexually or via blood transfusions.
The researchers also found that among students who had received both the vaccine and HBV immune globulin (antibodies), the infection rate was even higher, at 15 percent. The numbers were even higher among students who had received the immune globulin on an improper schedule, and among those whose mothers tested positive for HBeAg (another HBV protein that indicates the ability to transmit the disease).
Students who had not received the immune globulin were less likely to test positive for HBsAg the more of the vaccine they had received.
The researchers suggested that a booster vaccine might be needed at around age 15 to restore protection for those vaccinated as infants, especially those born to high-risk mothers or otherwise at high risk of exposure. They also suggested that a routine anti-HBV treatment could be given to pregnant women, although they acknowledged that neither the effectiveness nor safety of such a measure has yet been proven.