Fewer than four in 10 American adults have serologic immunity to hepatitis A, and roughly one in four has it for hepatitis B, according to a cross-sectional analysis published in JAMA Internal Medicine.
The study drew on the National Health and Nutrition Examination Survey and included hepatitis test results for 13,514 adults, a sample the researchers said represents about 226.1 million American adults. Immunity to hepatitis A was found in 39.5 percent, representing roughly 89.4 million people. Immunity to hepatitis B was found in 27.1 percent, with 25.2 percentage points of that attributable to vaccination.
Both vaccines have been available for decades, and both are highly effective. That combination—a good vaccine and a low share of protected adults—is the finding, and it is a coverage story rather than a vaccine performance story. An accompanying editorial in the same journal frames it as a policy problem rather than a scientific one.
The Distinction the Headline Number Hides
There is a gap between not having measurable antibodies and being unprotected, and it deserves more attention than it usually gets.
The analysis measured serologic immunity, defined as the presence of detectable antibodies in the blood at the time of testing. For hepatitis B in particular, antibody levels decline over years even in people who were fully vaccinated and mounted a good response. A review published this year in Mayo Clinic Proceedings argues that immune memory, rather than circulating antibody, predicts protection, noting that booster doses elicit rapid recall responses and that cohort studies report low or absent infection despite modest seroprotection rates.
That does not erase the finding. A person who never received the vaccine and a person whose antibodies have waned are both counted here as lacking immunity, and only the first group is clearly susceptible. The analysis establishes how many adults lack a measurable marker of protection. What it cannot establish is how many of those adults would actually become infected on exposure, or what infection rates will look like in the future.
The Coverage Problem Underneath the Serology
Independent data points in the same direction on the vaccination side, which is what makes the picture credible rather than an artifact of antibody testing.
Only about 30 percent of American adults are vaccinated against hepatitis B, according to a clinical review published in American Family Physician. That figure has barely moved for years, largely because the hepatitis B vaccination strategy was built around children. Coverage among children has been high since the 1990s, and the birth-dose and childhood series have driven large declines in infection in younger age groups, while adults were left to a risk-factor-based approach that clinicians found cumbersome.
Federal recommendations changed to address that. The CDC's advisory committee expanded hepatitis B vaccination to all adults aged 19 through 59, and to adults 60 and older with risk factors, and the agency has since recommended one-time screening for all adults. Uptake has lagged behind the recommendation.
Self-reported vaccination data also overstate coverage. A CDC analysis comparing survey responses with immunization records in Colorado health systems found moderate over-reporting for both hepatitis A and hepatitis B, with sensitivities of 52.5 percent and 43.4 percent, respectively, indicating that many people who report being vaccinated cannot be confirmed in records.
Reading the Study's Limits Before Its Conclusions
This is a cross-sectional analysis, which means it captured a single point in time and cannot show cause, direction, or trend within individuals.
The survey excluded groups at high risk for viral hepatitis, including people in prisons, so the estimates do not describe the populations where transmission is most concentrated. One author reported funding from Miromatrix, a company developing a therapy for liver conditions, a disclosure worth noting even though it does not directly bear on serology measurement.
Patterns within the data were consistent with what the vaccination history would predict. Hepatitis A immunity was more common among younger adults and among people born outside the United States. Hepatitis B immunity was likewise linked to younger age, tracking the cohorts that received childhood vaccination.
Current medical guidance has not changed as a result of this analysis. It documents a gap that recommendations already anticipated.
The Adults with the Strongest Reason to Ask
The two viruses spread differently, and that shapes who should act. Hepatitis A spreads through contaminated food or water and through close contact with an infected person, and it does not cause chronic liver disease, though it can cause severe acute illness. Hepatitis B spreads through blood and body fluids and can become chronic, raising the risk of cirrhosis and liver cancer. Roughly two-thirds of Americans with chronic hepatitis B do not know they have it.
Adults with the clearest reason to raise this at a routine visit include anyone who has never been screened for hepatitis B, adults aged 19 through 59 who cannot confirm vaccination, people with diabetes, chronic liver or kidney disease, HIV or a weakened immune system, people who inject drugs, household or sexual contacts of someone with hepatitis B, and anyone traveling to a region where either virus is common. Pregnant patients are screened for hepatitis B as standard care.
The practical step is small. Ask a clinician whether you have a documented vaccination history, and if not, whether screening or vaccination is appropriate for you. Both vaccines are covered without cost-sharing by most private insurance and Medicaid under preventive services rules, and local health departments often provide low-cost options for uninsured adults. Receiving an additional dose when prior doses cannot be documented is not harmful, and clinicians handle that situation routinely.
Federal vaccine recommendations for hepatitis A and B have been the subject of recent policy activity and litigation, and guidance could shift. MedicalDaily will report on any changes to the adult schedule.
Key Questions Answered
What did the analysis find? Serologic immunity to hepatitis A in 39.5 percent of US adults and to hepatitis B in 27.1 percent, based on test results for 13,514 adults representing about 226.1 million.
Does no measurable immunity mean I am unprotected? Not necessarily. Antibody levels decline over time even after successful vaccination, and immune memory may still respond to exposure. The analysis cannot distinguish between never-vaccinated and waned.
What kind of study is this? A cross-sectional analysis of national survey data. It describes a snapshot and cannot establish cause or predict future infection rates.
What are its main limitations? It excluded high-risk groups such as people in prisons, and one author disclosed funding from a company developing a liver therapy.
Has medical guidance changed? No. Recommendations already call for hepatitis B vaccination of all adults 19 through 59 and one-time screening for all adults.
Who should ask their doctor about this? Anyone who has never been screened for hepatitis B, adults who cannot confirm vaccination, people with diabetes, liver or kidney disease, HIV or immunosuppression, and travelers to areas where the viruses are common.
Is it harmful to get another dose if records are missing? No. Clinicians routinely vaccinate when prior doses cannot be documented.
