Vaccination programmes have reduced the prevalence of hepatitis B amongst children and younger adults in the US, the results of a large study in the July 15th edition of the Journal of Infectious Diseases show.
Investigators determined the prevalence of hepatitis B infection and immunity in representative samples of the US population between 1999 and 2006 and 1988 and 1994.
They found “a significant reduction of 68% hepatitis B virus prevalence in children”, and “a smaller, yet significant decrease in the prevalence of hepatitis B virus infection…among US-born adults 20-49 years of age.”
However, the researchers found enduring racial disparities in the prevalence of the infection.
The US has a relatively low prevalence of hepatitis B in comparison with some Asian countries, but due to its large population the absolute number of people infected with hepatitis B is considerable. Left untreated, hepatitis B infection may result in liver cancer or progressive liver disease in life.
In 1991, a strategy to eliminate transmission of the virus was implemented. All children are vaccinated against the infection, and the vaccine is also available to adults who have a high risk of acquiring the infection through their behaviour or occupation.
Investigators wished to assess trends in the prevalence of hepatitis B infection and immunity following the introduction of these vaccination programmes.
They therefore analysed individuals participating in the National Health and Nutrition Examination Survey (NHANES) in two time periods: 1999 to 2006 (27,000 individuals), and 1988 to 1994 (23,000 patients).
Blood samples from these individuals were tested for antibodies to hepatitis B core antigen (anti-HBc), and if the results were positive for hepatitis B surface antigen (HBsAg). Individuals in the 1999 to 2006 cohort were also tested for antibodies to hepatitis B surface antigen (anti-HBs).
Past or present infection with hepatitis B was defined as the presence of anti-HBc, and chronic infection was the presence of anti-HBc and HBsAg.
During the period 1999 to 2006, the overall prevalence of anti-HBc was 4.7%, with 0.27% of individuals having HBsAg.
These results were little different from the period 1988 to 1994 (5.4% and 0.38% respectively).
However, when the investigators stratified their results according to age and ethnicity, some important differences became apparent.
The prevalence of hepatitis B infection fell significantly amongst children aged between 6 and 19 years (from 1.9 to 0.6%, < 0.01), and amongst younger adults aged between 20 and 49 (from 5.9 to 4.6%, p < 0.05). By contrast, prevalence increased slightly amongst the over 50s (from 7.2 to 7.7%).
In addition, the investigators found a 79% reduction in the prevalence of chronic hepatitis B infection amongst children (0.24 to 0.05%), although this fall was not statistically significant.
Rates of past or current hepatitis B infections in 1999 to 2006 were higher amongst non-Hispanic blacks (12%) and individuals of other ethnicities (13%), than they were amongst whites (2.8%) and Mexican Americans (2.9%).
Furthermore, the investigators found that a significantly higher proportion of those born outside the US were infected with hepatitis B than those who were US-born (12.2% vs 3.5%).
Important as these disparities were, the investigators found that the prevalence of past and current infection decreased significantly between the two time periods in children of non-Hispanic black ethnicity (p < 0.05) and children of other ethnicities (p < 0.01).
Amongst adults aged 20 to 49, the fall in hepatitis B prevalence was only significant for those who were born in the US (p < 0.05). A pattern of decreasing prevalence was seen in all racial and ethnic groups, but was only significant for non-Hispanic blacks (p < 0.05).
In the 1999-2006 period, 23% of individuals had vaccine-induced immunity to hepatitis B. Immunity was highest amongst children (57%), followed by younger adults (17%), and was lowest amongst those aged over 50 (7.5%).
Prevalence of vaccine-induced immunity increased significantly – from 20.5% in the period between 1999 and 2002 to 25.2% during 2003 to 2006 (p < 0.001).
“In summary”, write the investigators “this analysis…provides new evidence of the impact of domestic and global childhood hepatitis B vaccination programs on preventing hepatitis B virus infections, while illustrating the large burden of chronic hepatitis B virus infection in the United States, which consists of approximately 730,000 persons.”
They conclude, “these results are relevant to public health policy makers and highlight the importance of ongoing hepatitis B vaccination programs and of programs to identify persons with chronic hepatitis B virus infection.”
Wasley A et al. The prevalence of hepatitis B virus infection in the United States in the era of vaccination. J Infect Dis 202: 192-201, 2010.