Joachim Mari¨en d,e, Solange Milolo c, Rachel Meta c, Junior Matangila c, Vivi Maketa c, Patrick Mitashi c, Jean-Pierre Van geertruyden b, Hypolite Muhindo-Mavoko c,
Pierre Van Damme has

a Center for the Evaluation of Vaccination, Vaccine and Infectious Disease Institute, University of Antwerp, Wilrijk, Belgium
b Global Health Institute, Department of Family Medicine and Population Health, University of Antwerp, Wilrijk, Belgium
c Tropical Medicine Department, University of Kinshasa, Kinshasa, Congo
d Department of Biology, Evolutionary Ecology group, University of Antwerp, Wilrijk, Belgium
e Department of Biology, Royal Museum for Central Africa, Tervuren, Belgium

ABSTRACT

Background: The long-term retention of information during the informed consent in clinical trials lasting over a year cannot be guaranteed for all volunteers. This study aimed to assess the level of participants' retention and understanding of the trial information after two years of participation in a vaccine trial.
Methods: In total, 699 health care providers (HCPs) and frontline workers were enrolled in the EBL2007 vaccine trial conducted between February 2019 and September 2022 in the Health District of Boende, Democratic Republic of the Congo (DRC). Individual scores obtained from a questionnaire (test of understanding, TOU), specifically designed to assess the understanding of the consent at baseline, were collected before the clinical trial started and at one-year and two-year intervals.
Results: TOU scores were high in the beginning of the trial (median TOU = 10/10), but significantly decreased in both the first and second years following (median TOU = 8/10 in year 1 and median TOU = 9/10 in year 2, pvalue < 0.0001). The decrease in scores was significantly higher among individuals with occupations requiring
shorter education such as midwives (median TOU = 7/10 in year 1 and 8/10 in year 2, pvalue = 0.025).
Furthermore, older participants exhibited poorer retention of information compared to younger individuals (median TOU = 8/10 vs 9/10, p-value = 0.007).
Conclusion: We observed a significant decline in the informational knowledge of informed consent, specifically in terms of basic knowledge on the study vaccine and trial procedures. As participant safety and understanding is a paramount ethical concern for researchers, it is crucial for participants to fully understand the study's objectives
and potential risks. Therefore, our findings suggest the need for clinical researchers to re-explain participants to optimize the protection of their rights and wellbeing during the research.

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