HUMORAL AND CELLULAR IMMUNE MEMORY RESPONSE 12 YEARS AFTER SINGLE DOSE VACCINATION AGAINST HEPATITIS A IN ARGENTINIAN CHILDREN

GONZALEZ JORGE; VIZZOTTI CARLA; URUEÑA A; BARÉ PATRICIA; BADANO MARÍA NOEL; FINK SUSANA

Congreso; 39th Annual Meeting of the European Society for Paediatric Infectious Diseases; 2020

Background: Infants' universal HAV single-dose vaccination has been highly effective for controlling HAV infection in Argentina, and in many other Latin-American countries that adopted that strategy. Although antibodies wane over time, this has not been associated with HAV outbreaks or breakthrough infections, suggesting a relevant role for memory immunity. This study aimed to assess long term humoral and cellular immune memory response after HAV single-dose vaccination. Methods: We selected HAV-single dose vaccinated individuals known to have, in a 2015 study, protective (PAL)or unprotective antibody levels (UAL) against HAV. Humoral memory response was assessed by measuring anti-HAV Ab titers at admission in both groups, and 30 days after a booster dose in the UAL group. Flow cytometry analysis of peripheral blood mononuclear cell (PBMC) sample stimulated with HAV antigen was performed to identify activated CD4+ memory T cells (CD3+CD4+CD69+CD45RO+) or CD8+ memory T cells (CD3+CD8+CD69+CD45RO+).Results: 48/52 (92%) individuals from UAL group who completed follow up reached protective levels after booster dose. In the PAL group, 2/27 (7%) individuals waned HAV Abs lacking seroprotection, while in 25/27 (93%) Abs remained >10 mUI/mL. HAV-specific memory CD4+ T cells were detected in 25/47 (53.2%) subjects while HAV-specific memory CD8+ T cells were observed in 16/47 (34.04%) individuals. HAV-specific memory CD4+ and CD8+ T-cells was observed in 14/25 (56%) individuals with non-detectable anti-HAV Ab levels, showing that the presence of memory T-cells was independent of the level or presence of anti-HAV antibodies. Conclusions: Long-term immunity demonstrated in the present work, including or not antibody persistence, suggests that individuals with waned Ab titers may still be protected and supports the single-dose HAV strategy.