Immune memory in hepatitis E virus: a comparative study of natural infection and vaccination in a nursing home population

Immune memory is crucial for preventing hepatitis E virus (HEV) infection. Our study aims to investigate immunological memory characteristics and differences between vaccination and natural HEV infection, taking into account that both can induce immune memory. We recruited 60 HEV-infected patients, 58 contingency HEV-vaccinated individuals and 4 controls from an outbreak of hepatitis E in a nursing home between June and August 2023. Multicolor flow cytometry, ELISA, and quantitative polymerase chain reaction (qPCR) were employed to detect memory T-cell expression profiles, HEV-specific antibodies and cytokine expression. We observed that the level of HEV-specific IgM in acute jaundiced hepatitis E patients was greater than that in non-jaundiced patients (8.37 ± 1.27 vs. 4.27 ± 0.81, P < 0.05). No significant differences were detected in the HEV-specific IgG and memory T cell expression profiles among the different severities of hepatitis E. The percentage of CD8+ TEM at 6 months after recovery was significantly greater than that in acute jaundice patients (1.60% ± 0.30% vs. 1.15% ± 0.35%, P < 0.05). Compared with natural infection, three-dose vaccination increased the level of HEV-specific IgG (14.97 ± 0.21 vs. 12.75 ± 0.37, P < 0.05), IL-7 and IL-15 (28.50 ± 3.82 vs. 23.32 ± 6.37, 608.60 ± 143.30 vs. 257.50 ± 69.87, P < 0.05). Natural infection could effectively establish immune memory. During convalescence, infection severity impacted only HEV-specific IgM, while HEV-specific IgG and memory T-cell expression profiles were not affected. Compared with natural infection, three-dose vaccination results in equal effective humoral immune memory and weaker cellular immune memory with minimal side effects.