Reduced HAV IgG Seropositivity Among Unvaccinated People Living with HIV: The Weak Shield.

People living with HIV (PLWH) represent a high-risk population for hepatitis A virus (HAV) infection, with exposure risk equal to or higher than that of the general population, particularly within adult risk networks. Anti-HAV immunoglobulin G (IgG) serves as a neutralizing antibody and is considered a key marker of protective immunity against HAV infection. However, the serologic profile of anti-HAV IgG and IgM among unvaccinated PLWH remains insufficiently characterized, especially in South China. A total of 1232 unvaccinated adults were enrolled in the study, including 800 PLWH and 432 HIV- negative controls, to evaluate the serological markers of HAV immunity. Serum anti-HAV IgG and immunoglobulin M (IgM) were measured using enzyme-linked immunosorbent assays, and demographic, immunological, and biochemical data were collected. We observed that PLWH had significantly lower anti-HAV IgG concentrations (0.27 ± 0.16 vs. 0.31 ± 0.14 ng/mL, p < 0.001) and a lower IgG seropositivity rate (22.5% vs. 35.6%, p < 0.001) compared with HIV-negative controls, whereas no differences were found in IgM levels or positivity between the two groups. Multivariable logistic regression identified HIV infection (OR = 0.599, 95% CI 0.413-0.869, p = 0.007) and age (OR = 1.019, 95% CI 1.007-1.031, p = 0.002) as independent factors associated with IgG seropositivity. Among PLWH, those who were IgG-positive tended to be older (p = 0.003) and had higher serum globulin levels (p < 0.001), whereas IgM positivity was linked to younger age (p < 0.001) and a higher CD4/CD8 ratio (p = 0.030). Age-stratified analyses further revealed that IgG seroprevalence increased with age, while IgM positivity showed a declining trend. These findings indicate a considerable immunity gap in a population at elevated risk of HAV infection and support the need for targeted serologic screening and vaccination strategies among PLWH.