Adherence to a Vaccination Schedule in a Simulated HIV Vaccine Efficacy Trial Among Adults in Fishing Communities Around Lake Victoria, Uganda

Background/Objectives: Fishing communities (FCs) around Lake Victoria have been identified as suitable for future HIV vaccine efficacy trials due to their high HIV incidence rates. To inform trial design and implementation, we evaluated adherence to vaccination schedules and study retention in a simulated HIV vaccine efficacy trial (SiVET) among adults from two fishing communities in Uganda. Methods: A 12-month prospective cohort study enrolled 250 HIV seronegative adults, aged 18–49 years, from one island and one mainland FC. The hepatitis B vaccine was administered at months 0, 1, and 6 to simulate an HIV vaccine regimen. Those testing HIV positive or pregnant were referred for care. Socio-demographic, behavioral, and clinical data were collected at baseline, 6, and 12 months. Poisson regression models with robust standard errors were used to identify factors associated with vaccination completion and retention. Results: Participants’ age ranged between 25–34 years, with a mean age of 27.6 years (SD = 6.4), and 68% of participants were from the mainland and 22% from the island. The overall vaccination completion rate was 86.5 per 100 person-years of observation (PYO), and was similar between mainland (86.8/100 PYO) and island dwellers (85.6/100 PYO). Male participants were likelier to complete all vaccinations [aRR = 1.1 (95% CI 1.0–1.2)]. Having received a secondary education or higher was also associated with higher vaccination completion compared to the rates for those with primary or no formal education [aRR = 1.1; 95% CI: 1.0–1.2]. Notably, participants who reported illicit drug use [aRR = 1.3; 95% CI: 1.2–1.4] and those engaged in paid sex [aRR = 1.2; 95% CI: 1.1–1.4] were more likely to complete all study visits. Conclusions: Adherence to vaccination schedules was high and consistent between mainland and island populations. These findings confirm that fishing communities are well-suited for future HIV vaccine efficacy trials. Predictors of adherence include male sex, secondary education, illicit drug use, and involvement in paid sex. High adherence rates underscore the feasibility of conducting such trials in this population.