Long‐term stability of human parvovirus B19 neutralizing antibody titer trends in donor‐derived pooled plasma and plasma‐derived immunoglobulin product lots in Japan

Abstract Background Human parvovirus B19 (B19) is a major pathogen involved in transfusion‐related infections. In Japan, B19 antigen screening is conducted during blood donation, and B19 deoxyribonucleic acid (DNA) levels in pooled plasma have remained below the limit recommended by the U.S. Food and Drug Administration (10 4 IU/mL). Anti‐B19 neutralizing antibodies mitigate the risk of transmission via blood products. We assessed anti‐B19 neutralizing antibody titers and trends in pooled plasma and immunoglobulin products in Japan. Study Design and Methods Anti‐B19 neutralizing antibody titers (NT50) were assayed in vitro using cultured human leukemia KU812 cells. Anti‐B19 NT50, immunoglobulin G (IgG) concentrations, and B19 DNA level trends were evaluated in donor‐derived pooled plasma in Japan. Anti‐B19 NT50 and IgG concentrations of immunoglobulin products were also assessed longitudinally. Results Pooled plasma lots contained sufficient neutralizing antibodies to eliminate the infectivity of up to 10 8.2 IU/mL of B19 in vitro. Anti‐B19 NT50 remained stable over the past decade, even during the Coronavirus disease 2019 (COVID‐19) pandemic, when erythema infectiosum cases decreased. B19 DNA levels were undetectable shortly after the pandemic but have exhibited an upward trend since late 2024, coinciding with a recent increase in reported cases. Discussion In Japan, the neutralizing properties of donor‐derived pooled plasma remained stable and functionally comparable to those reported overseas. Stable neutralizing titers, alongside B19 antigen screening, ensure effective protection against B19 transmission. Continuous monitoring of DNA levels and neutralizing titers remains critical for the timely detection of unpredictable epidemiological changes.