Background: The Philippines is hyperendemic for hepatitis B infection. Vaccination is crucial for protection.  Local data on the antibody response after completion of the primary vaccination series is limited.

Objective: This study aimed to measure the anti-HBs levels among college students who completed primary hepatitis B vaccination series, compare seropositivity across stratified groups and correlate anti-HBs levels with the time elapsed since the last vaccine dose.

Methods: This cross-sectional study included 111 college students in health-related courses with immunization record showing the complete primary Hepatitis B vaccination series. Participants were stratified based on the following vaccination schedules: 0-1-6-month group; 0-1-2-month group; and booster group. Anti-HBs titers were determined.

Data Analysis: Statistical analyses included One-way ANOVA, Kruskal-Wallis test, Fisher’s Exact test and Shapiro-Wilk normality test. Kaplan-Meier Survival Estimate assessed the probability of anti-HBs seropositivity over time.  Data were analyzed using STATA 13.1.

 The baseline characteristics of the study population were homogenous.  The median anti-HBs titer several years after primary vaccination was low at 2.9 mIU/mL. Participants in the booster group had the highest seropositivity rate (57.14%) with a median titer of 30.16 mIU/mL. There was an inverse relationship between anti-HBs titer and elapsed time since the last vaccine dose. Kaplan-Meier Survival Estimate showed that the seropositivity decreases to 90.56% after 15.8 years, 51.3% after 17.5 years, and 2.97% at 1Results:8 years.

Conclusion: This study revealed low anti-HBs titers among students who previously completed primary vaccination series, with no significant difference between two schedules. Booster doses resulted in the highest seropositivity. Over-all, seropositivity declines over time.

Jay Ron O. Padua is a board-certified pediatrician and infectious disease specialist in the Philippines. He earned his Doctor of Medicine from the University of Santo Tomas (UST). He completed his residency in Pediatrics at UST Hospital and fellowship in Pediatric Infectious Diseases at the Philippine Children’s Medical Center. Dr. Padua demonstrated consistent academic and clinical excellence, highlighted by his leadership positions and top performance in professional examinations. He has pursued advanced training in pediatric HIV, dengue, and tropical medicine through observerships and programs at renowned institutions such as Texas Children’s Hospital, Chiang Mai University, Mahidol University, and St. Jude Children’s Research Hospital.  Dr. Padua has contributed significantly to pediatric infectious diseases through diverse studies and presentations. His notable works include a retrospective cohort study on empiric antibiotic outcomes in pediatric acute lymphoblastic leukemia with multiple international poster presentations and publication in a peer-reviewed journal. He co-authored studies on HIV prevention, dengue diagnosis, Hepatitis B seropositivity, and SARS-CoV-2 transmission, earning recognition in research contests. His publications cover topics like pediatric COVID-19, community-acquired pneumonia, and antimicrobial stewardship. He has played key roles in developing clinical practice guidelines for pediatric pneumonia and Wilms’ tumor and has ongoing studies on COVID-19 severity. His professional affiliations span numerous hospitals and societies, where he serves in leadership, advisory, and educational capacities, such as chairing committees on HIV, infection control, and antimicrobial stewardship. A sought-after speaker, he has delivered lectures on dengue, immunization, and vaccine-preventable diseases at national and international forums.