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Despite the successful introduction of oral cholera vaccines, Zambia continues to experience multiple, sporadic, and protracted cholera outbreaks in various parts of the country. While vaccines have been useful in staying the cholera outbreaks, the ideal window for re-vaccinating individuals resident in cholera hotspot areas remains unclear. Using a prospective cohort study design, 225 individuals were enrolled and re-vaccinated with two doses of Shanchol™, regardless of previous vaccination, and followed-up for 90 days. Bloods were collected at baseline before re-vaccination, at day 14 prior to second dosing, and subsequently on days 28, 60, and 90. Vibriocidal assay was performed on samples collected at all five time points. Our results showed that anti-LPS and vibriocidal antibody titers increased at day 14 after re-vaccination and decreased gradually at 28, 60, and 90 days across all the groups. Seroconversion rates were generally comparable in all treatment arms. We therefore conclude that vibriocidal antibody titers generated in response to re-vaccination still wane quickly, irrespective of previous vaccination status. However, despite the observed decline, the levels of vibriocidal antibodies remained elevated over baseline values across all groups, an important aspect for Zambia where there is no empirical evidence as to the ideal time for re-vaccination. [ABSTRACT FROM AUTHOR]

Cholera is responsible for 1.3 to 4.0 million cholera cases globally and poses a significant threat, with Zambia reporting 17,169 cases as of 4th February 2024. Recognizing the crucial link between natural cholera infections and vaccine protection, this study aimed to assess immune responses post cholera infection and vaccination. This was a comparative study consisting of 50 participants enrolled during a cholera outbreak in Zambia's Eastern Province and an additional 56 participants who received oral cholera vaccinations in Zambia's Central Province. Vibriocidal antibodies were plotted as geometric mean titres in the naturally infected and vaccinated individuals. A significant difference (p < 0.047) emerged when comparing naturally infected to fully vaccinated individuals (2 doses) on day 28 against V. cholerae Ogawa. Those who received two doses of the oral cholera vaccine had higher antibody titres than those who were naturally infected. Notably, the lowest titres occurred between 0-9 days post onset, contrasting with peak responses at 10-19 days. This study addresses a critical knowledge gap in understanding cholera immunity dynamics, emphasizing the potential superiority of vaccination-induced immune responses. We recommend post infection vaccination after 40 days for sustained immunity and prolonged protection, especially in cholera hotspots., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)