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
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
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%
"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