Hepatitis B virus (HBV) remains one of the world’s most consequential pathogens. An estimated 254 million people were living with chronic HBV infection in 2022, and roughly 1.1 million deaths were attributed to the virus that year. China carries the heaviest national burden, with approximately 75 million infected individuals. Chronic infection drives cirrhosis and hepatocellular carcinoma (HCC), but accumulating evidence also links chronic HBV to elevated risks of digestive system malignancies, kidney disease, and mortality from cardiovascular and cerebrovascular conditions compared with the general population. Against this backdrop, the World Health Organization has endorsed a global strategy to eliminate viral hepatitis by 2030, emphasizing both the prevention of new infections and the expansion of diagnosis and treatment to reduce mortality among those already infected.

Loss of HBsAg is the central therapeutic goal in chronic hepatitis B and underpins the treatment endpoint known as functional cure. Spontaneous HBsAg seroclearance also occurs during the natural course of infection, though infrequently — roughly 1 percent of patients per year. Prior research has consistently shown that patients who clear HBsAg experience substantially lower rates of cirrhosis and HCC. What remained uncertain, however, was whether seroclearance is also associated with overall survival and, in particular, with extrahepatic mortality from cancers and cardiovascular disease — a question of growing importance as the population of people living with chronic hepatitis B ages and accumulates comorbidities.

To address this gap, investigators drew on the Chronic Hepatitis B Infection and Liver Disease (HEPCARE) study, a multicenter, prospective, community-based cohort in Jiangsu Province. Participants were recruited through serological surveys conducted between September 2009 and November 2010 and were required to be HBsAg-positive, hepatitis C antibody-negative, and free of cirrhosis and liver cancer at enrollment. Because HBV DNA measurements began at the 2012 follow-up, the analysis defined 2012 as baseline and followed participants through December 2023, with assessments in 2012, 2013, 2014, 2016, 2018, 2020, and 2023. After exclusions, 6551 participants entered the analytical pool, and after propensity score matching on age, sex, region, and baseline antiviral treatment status, the final matched cohort comprised 1029 individuals who achieved sustained HBsAg seroclearance with HBV DNA below 100 IU/mL and 2931 who remained persistently HBsAg-positive.

A key methodological strength of the study lies in its handling of time. HBsAg seroclearance is a time-dependent event that occurs during follow-up, and conventional analyses that treat it as a fixed baseline characteristic are vulnerable to immortal time bias, which can distort survival estimates. By conducting regular interval surveillance and using time-dependent Cox regression, the researchers could allocate person-time accurately according to each participant’s changing serovirological status. The exposure itself was stringently defined: seroclearance required HBsAg negativity together with HBV DNA below the quantification limit of 100 IU/mL, confirmed at two or more consecutive follow-up visits, with participants whose profiles suggested occult hepatitis B infection excluded to avoid misclassification.

The results were striking across multiple outcome domains. Over a median follow-up of roughly 11 years, participants who achieved sustained seroclearance had significantly lower incidence rates of cirrhosis (2.02 versus 3.97 per 1000 person-years) and HCC (2.97 versus 4.97 per 1000 person-years). In fully adjusted time-dependent Cox models, seroclearance was associated with a 55 percent lower hazard of cirrhosis (adjusted hazard ratio 0.45) and a 48 percent lower hazard of HCC (adjusted hazard ratio 0.52). Mortality told a similar story: 64 deaths occurred in the seroclearance group compared with 405 in the persistent infection group, corresponding to incidence rates of 7.55 and 12.17 per 1000 person-years, and seroclearance was associated with a 53 percent lower hazard of all-cause mortality (adjusted hazard ratio 0.47).

Perhaps the most novel findings concerned cause-specific mortality. Among the 469 deaths in the matched population, 146 were attributed to extrahepatic cancers, 117 to cardiovascular disease, and 112 to liver-related causes. Sustained seroclearance was associated with lower hazards of liver-related mortality (adjusted hazard ratio 0.46), extrahepatic cancer-related mortality (0.51), and cardiovascular mortality (0.56), with the strongest association observed for digestive system cancer-related mortality. When competing risks were formally accounted for using Fine–Gray subdistribution hazard models, these associations persisted for cirrhosis, HCC, liver-related mortality, and extrahepatic cancer-related mortality, and model-standardized cumulative incidences at 10 years were consistently lower in the seroclearance state for all major endpoints examined.

The investigators then asked whether HBsAg loss carries prognostic information beyond viral DNA suppression alone — a clinically important question, since suppressing HBV DNA below 100 IU/mL is a conventional treatment goal. In an analysis treating serovirological status as a three-state time-varying variable, the HBsAg-negative state with very low HBV DNA was associated with lower hazards of cirrhosis, HCC, all-cause mortality, extrahepatic cancer mortality, and cardiovascular mortality compared with the HBsAg-positive state at similarly low viral loads. Conversely, isolated HBV DNA suppression without seroclearance was not associated with lower extrahepatic mortality. Additional weighting analyses incorporating baseline HBV DNA attenuated the HCC estimate somewhat, suggesting that part of that association depends on differences in baseline viral burden, but the associations with all-cause and extrahepatic cancer mortality remained statistically significant.

To translate the associations into population-level terms, the team estimated population attributable fractions and restricted mean survival time. Persistent infection was associated with attributable fractions of approximately 48 percent for cirrhosis, 47 percent for liver-related mortality, 42 percent for all-cause mortality, 41 percent for HCC, 40 percent for extrahepatic cancer mortality, and 35 percent for cardiovascular mortality. Using age as the time scale, restricted mean survival time was estimated at 83.21 years in the seroclearance state versus 78.04 years in the persistent infection state — a 5.17-year difference within the observed age range, with the survival advantage widening notably after age 60. Sex-stratified analyses suggested that these inverse associations were generally stronger in men, with statistically significant interactions for all-cause and liver-related mortality, echoing prior evidence that men with chronic hepatitis B tend to experience less favorable long-term outcomes than women.

The authors caution that most seroclearance events in the cohort occurred spontaneously rather than through antiviral therapy, so the findings primarily reflect the prognosis associated with spontaneous HBsAg loss, which may partly reflect a favorable underlying viral-host profile and overall health status. Residual confounding from unmeasured factors such as socioeconomic status and healthcare utilization cannot be excluded, the assay’s quantification limit of 100 IU/mL may have classified some low-level viremia as undetectable, and the single-province, community-based design warrants validation in other populations, including cohorts enriched for treatment-induced functional cure. Biologically, the authors propose that persistent viral antigen exposure and chronic immune activation may impair tumor immune surveillance and promote systemic inflammation, whereas HBsAg clearance accompanies a marked reduction in antigen burden and partial restoration of HBV-specific immune responses — hypothesis-generating mechanisms that require further study. Nevertheless, the consistency of the associations across competing-risk models, three-state analyses, and extensive sensitivity analyses, combined with the substantial attributable burden and survival differences, positions sustained HBsAg seroclearance with very low HBV DNA as an informative long-term prognostic marker in chronic hepatitis B, and underscores the potential population health value of broader attainment of this serovirological state.

Subject of Research: HBsAg seroclearance and long-term hepatic and extrahepatic mortality risks in chronic hepatitis B

Article Title: HBsAg seroclearance with HBV DNA <100 IU/mL and long-term risks of adverse liver events, all-cause mortality, and cause-specific mortality in chronic hepatitis B: a prospective cohort study

Article References: Zhang, Y., Yao, W., Jiang, J., Qian, J., Chen, X., Jiang, Q., Yan, Y., Wang, S., Bai, H., He, C., Zhu, L., Jiang, T., Hu, Z., Shen, H., Zhai, X., & Song, C. (2026). HBsAg seroclearance with HBV DNA <100 IU/mL and long-term risks of adverse liver events, all-cause mortality, and cause-specific mortality in chronic hepatitis B: a prospective cohort study. The Lancet Regional Health – Western Pacific, 74, Article 101983. https://doi.org/10.1016/j.lanwpc.2026.101983

Image Credits: AI Generated

DOI: 10.1016/j.lanwpc.2026.101983

Keywords: hepatitis B, HBsAg seroclearance, functional cure, hepatocellular carcinoma, cirrhosis, all-cause mortality, extrahepatic cancer, cardiovascular mortality, HBV DNA, prospective cohort, population attributable fraction, chronic hepatitis B

The epidemiological picture painted by the review is strikingly heterogeneous. In the general population of low-endemicity countries, OBI prevalence can be as low as 0.8 percent. But in groups with concurrent viral infections the figure climbs steeply: more than 10 percent of individuals co-infected with hepatitis C virus or HIV carry occult HBV. The rate exceeds 40 percent among people with an isolated positive antibody to hepatitis B core antigen, a serological fingerprint of past exposure that persists long after surface antigen vanishes. A systematic review cited in the article found occult infection in adults across every region studied, and separate analyses in children show that babies born to surface-antigen-positive mothers can acquire OBI despite vaccination and hepatitis B immunoglobulin prophylaxis. These numbers matter because they define the size of the reservoir from which transfusion transmission, reactivation and, potentially, liver cancer can emerge.

Understanding how OBI arises requires a brief excursion into HBV biology. The virus maintains a persistent intermediate known as covalently closed circular DNA, or cccDNA, a minichromosome that resides in the nucleus of infected hepatocytes and serves as the transcriptional template for all viral RNAs. When surface antigen seroclearance occurs, whether spontaneously, after antiviral therapy or following recovery from acute infection, cccDNA is not eradicated. Instead it is transcriptionally silenced by epigenetic mechanisms, including histone deacetylation and methylation changes orchestrated by host factors such as SIRT3 and opposed by viral HBx protein recruits like LSD1 and Set1A. Integrated HBV DNA in the host genome can also persist independently of cccDNA, and both forms have been detected in the livers of patients classified as serologically recovered. The review emphasises that OBI therefore represents a spectrum of viral persistence rather than a single entity, arising either after HBsAg seroclearance in formerly chronically infected patients or after resolution of acute infection.

Why does surface antigen fall below detectable levels while viral DNA persists? The review details several converging mechanisms. Mutations in the PreS/S gene of the virus can alter or truncate the surface protein so that commercial assays fail to recognise it, a phenomenon known to account for a subset of occult infections. Viral variants carrying deletions in the X gene have been found in vaccinated individuals with OBI, suggesting immune selection pressures shape the hidden viral population. Host epigenetic silencing of cccDNA suppresses surface antigen expression to vanishingly small amounts, and newer ultrasensitive assays have shown that some patients previously labelled seronegative in fact have extremely low-level surface antigen detectable at concentrations below the standard cut-off of 0.05 IU/ml. This observation carries a conceptual twist: with sufficiently sensitive assays, some occult infections might be reclassified as overt infection, blurring the boundary between the two states.

Diagnosis remains the most technically demanding aspect of OBI. Serum HBV DNA levels in occult infection are typically extremely low and fluctuate over time, often dipping below the detection limits of routine commercial polymerase chain reaction assays. Hepatitis B core antibody, the single most useful serological marker, indicates prior exposure with a sensitivity of 77 percent and a specificity of 76 percent for seropositive occult infection, but it cannot by itself confirm active viral persistence. Liver tissue offers the definitive answer, since intrahepatic cccDNA is the hallmark of the condition, yet liver biopsy is rarely justifiable for diagnosis alone. The methodological frontier lies in droplet digital PCR, which partitions samples into thousands of nanolitre-scale reactions and enables absolute quantification of scarce DNA templates. Recent studies have validated high-sensitivity droplet digital PCR assays for both serum HBV DNA and intrahepatic cccDNA, and the review argues these platforms are reshaping what clinicians can detect. Complementary biomarkers such as hepatitis B core-related antigen and serum HBV RNA, which reflect cccDNA transcriptional activity, are being evaluated as non-invasive windows into occult viral replication.

The clinical consequences of undetected occult infection fall into three major categories. The first is transmission. Documented cases show HBV has been transmitted through transfusion of blood products and through solid organ transplantation from donors with occult infection, sometimes with devastating outcomes for immunosuppressed recipients. Analysis of transmission events has forced a revision of the minimal infectious dose, revealing that even very low viral loads in donated blood can establish infection. Nucleic acid testing of blood donations has reduced but not eliminated this risk, and the review discusses the ongoing international debate over whether anti-HBc screening of donors should be adopted more widely, weighing improved safety against the loss of otherwise suitable donors in endemic regions.

The second category is reactivation. Patients with occult HBV who receive immunosuppressive therapy, particularly B-cell-depleting agents such as rituximab, but also corticosteroids, ibrutinib, abatacept, temozolomide and therapies used in haematopoietic stem cell transplantation, are at risk of reverse seroconversion, in which surface antigen reappears and viral replication surges, occasionally causing fulminant hepatic failure. Quantification of core antibody titres may help stratify risk among patients with resolved infection, and international guidelines from the AASLD, AGA and EASL converge on the recommendation that individuals with serological evidence of prior HBV exposure should receive prophylactic nucleoside analogue therapy before high-risk immunosuppression. The review stresses that occult carriers are precisely the patients in whom routine serological screening fails, underscoring the importance of anti-HBc testing before oncological and rheumatological treatments.

The third and most debated consequence is oncogenesis. In patients with cryptogenic cirrhosis and cryptogenic hepatocellular carcinoma, studies have repeatedly found occult HBV DNA, cccDNA and viral integration events within tumour and surrounding liver tissue. A high proportion of patients with undetectable surface antigen and hepatocellular carcinoma harbour HBV DNA integrated into hepatocyte genomes, sometimes without cirrhosis, and integrations that reshape genomic structure have been shown to promote carcinogenesis through insertional mutagenesis and dysregulation of oncogenes such as those on chromosome arms recurrently targeted in the cancer genome surveys. The review also describes associations between occult infection and accelerated fibrosis in chronic hepatitis C, more severe outcomes in non-alcoholic fatty liver disease, and a prediction of non-alcoholic steatohepatitis in severely obese individuals. Nevertheless, the authors are careful to note that routine OBI screening is not recommended for milder chronic liver disease of other causes, and that the oncogenic potential of occult infection requires further study before screening policies change.

Management of confirmed OBI follows a deliberately targeted approach. The review recommends that OBI be excluded in individuals presenting with cryptogenic cirrhosis or hepatocellular carcinoma, and that treatment with a nucleoside analogue be initiated if occult infection is confirmed. For transplant medicine, grafts from anti-HBc-positive donors can be used with appropriate antiviral prophylaxis and monitoring, a strategy supported by systematic reviews showing acceptable recipient outcomes in liver, kidney and heart transplantation. For blood services, nucleic acid testing in minipool or individual-donation formats, alongside cost-effectiveness modelling from centres such as Shandong Blood Center in China, informs the evolving balance between transfusion safety and blood supply. What remains conspicuously unresolved is the management of the millions of anti-HBc-positive individuals worldwide who have no evidence of active replication and no need for treatment, yet who carry a dormant viral archive whose clinical behaviour over a lifetime is only beginning to be characterised.

The review closes with a set of challenges that will define the next decade of occult HBV research. Ultrasensitive surface antigen assays may reclassify part of the occult reservoir, forcing a redefinition of the disease boundary. Standardisation of droplet digital PCR for cccDNA and serum DNA, harmonisation of HBV RNA and core-related antigen measurements, and the incorporation of viral integration mapping into clinical phenotyping are all identified as priorities. As functional cure strategies for chronic hepatitis B, built around HBsAg seroclearance, move into large trials, the review’s central message acquires added urgency: seroclearance is not viral eradication. Every patient whose surface antigen disappears may still harbour replication-competent virus, and the systems of blood banking, transplant medicine, oncology and hepatology must be designed with that hidden reservoir in mind.

Subject of Research: Occult hepatitis B virus infection, the persistence of replication-competent HBV DNA in liver or blood of hepatitis B surface antigen-seronegative individuals

Article Title: Occult hepatitis B virus infection

Article References: Mak, L.-Y., Hui, R. W.-H., Pollicino, T., Cornberg, M., Gish, R., Jacobson, I., Kennedy, P. T., Seto, W.-K., Raimondo, G., & Yuen, M.-F. (2026). Occult hepatitis B virus infection. Nature Reviews Gastroenterology & Hepatology. https://doi.org/10.1038/s41575-026-01257-x

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DOI: 10.1038/s41575-026-01257-x

Keywords: occult hepatitis B, hepatitis B virus, HBV DNA, cccDNA, hepatitis B surface antigen, anti-HBc, hepatocellular carcinoma, HBV reactivation, droplet digital PCR, blood transfusion transmission, liver transplantation, nucleoside analogues