Although nearly 70 million people in the US have been vaccinated against hepatitis B virus (HBV), there are still 847,000 people with evidence of infection, about 400,000 of whom are Asian, according to the latest National Health and Nutrition Examination Survey (NHANES) results published in the February edition of Hepatology.
Hepatitis B virus is transmitted via blood, sexual contact and mother-to-child transmission during pregnancy or delivery. HBV is endemic in parts of East Asia and Africa, and people who come from these regions have higher rates of infection. About 90% of people infected as adults clear the virus naturally, but most of those infected as infants develop chronic infection.
An effective HBV vaccine became available in the early 1980s and is now part of the routine childhood immunisation series in many countries. Hepatitis B can be treated with antivirals or interferon, but these usually do not lead to a cure. Over years or decades, hepatitis B can cause serious liver disease including cirrhosis and hepatocellular carcinoma.
Henry Roberts from the US Centers for Disease Control and Prevention (CDC) Division of Viral Hepatitis and colleagues analysed hepatitis B prevalence data from NHANES, an ongoing study assessing the health of adults and children in the US. As a household survey, NHANES does not include homeless people, prisoners, active duty military personnel or people living in long-term care facilities – groups with higher than average HBV infection rates.
Chronic hepatitis B prevalence in the US is affected by the shrinking number of young people who are susceptible to infection as vaccination coverage rises. It is estimated that about 25% of the overall US population – but 90% of young children – have vaccine-induced immunity, the authors noted as background. However, this is offset by people immigrating from countries where the virus is endemic. An estimated 3.9 million foreign-born people from these countries currently reside in the US, and they may account for as many as 70% of all hepatitis B cases.
Roberts and his team analysed hepatitis B prevalence estimates among non-institutionalised people aged 6 years and older during three NHANES study periods: 1988-1994 (21,260 people), 1999-2008 (29,828 people) and 2007-2012 (22,358 people). Because their numbers in the population are small, the survey 'over-sampled' Asian people starting in 2011-2012.
NHANES participants completed interviews, underwent medical examinations and provided blood samples for testing. Prevalence was determined by serological testing looking at:
- Hepatitis B surface antigen (HBsAg), indicative of chronic infection (or, more rarely, acute infection)
- Antibodies to hepatitis B core antigen (anti-HBc), indicating having ever been infected with HBV
- Antibodies to hepatitis B surface antigen (anti-HBs) without anti-HBc, indicating immunity due to vaccination.
The prevalence of positive anti-HBc, indicating past or present HBV infection, declined steadily over time, from 5.3% during 1988-1994 to 4.8% during 1999-2006 to 3.9% during 2007-2012. Based on these unadjusted prevalence estimates, 12.1 million, 12.5 million and 10.8 million non-institutionalised US residents had ever been infected with HBV during the three time periods.
Looking at chronic HBV infection, the overall prevalence has remained fairly steady over time, with an adjusted prevalence of 0.3% since 1999. Most chronic infections were seen in the 20-49 and 50 and older age groups. However, among people younger than 20 years – those most likely to have been vaccinated – chronic HBV prevalence declined significantly, from 0.2% during 1988-1994 to 0.03% during 2007-2012.
The prevalence of chronic HBV infection among black US residents was 2- to 3-fold greater than that of the overall population. Chronic hepatitis B prevalence among Asian people in the US was 3.1% during 2011-2012, or 10-fold greater than the overall population.
Estimating the number of chronically infected people from the HBV prevalence in each racial/ethnic group led the researchers to conclude that there were 847,000 people with chronic hepatitis B in 2011-2012 (range 565,000-1,130,000). Approximately 400,000 of these – or nearly half – were Asian.
Adjusted prevalence of vaccine-induced immunity increased 16% overall, from 21.7% during 1999-2006 to 25.1% during 2007-2012. Based on these estimates, the number of people protected by vaccination rose from 57.8 to 68.5 million. Among children and young adults (ages 6-19), however, the adjusted prevalence of vaccine-induced immunity fell somewhat, from 56.8% in during 1999-2006 to 44.4% during 2007-2012.
"Despite increasing immune protection in young persons vaccinated in infancy, an analysis of chronic hepatitis B prevalence in racial and ethnic populations indicates that during 2011-2012, there were 847,000 HBV infections (which included about 400,000 non-Hispanic Asians) in the non-institutionalized US population," the study authors concluded.
"The findings in this study provide further evidence that migration of HBV-infected persons from HBV endemic countries has largely contributed to prevalence rates remaining constant since 1999," they noted. "Recommendations, released by the Institute of Medicine in 2010, advised the CDC and other federal agencies to expand screening and vaccination hepatitis programs that target foreign-born populations."
Roberts H et al. Prevalence of chronic hepatitis B virus (HBV) infection in U.S. households: National Health and Nutrition Examination Survey (NHANES), 1988-2012. Hepatology 63(2):388-397, February 2016.