Effectiveness of single-dose use of oral cholera vaccine towards reducing cholera incidence and severity during the 2022-2023 in Malawi; A cross-sectional study

Background Approximately 59,000 cases and 1700 deaths were reported during the 2022-2023 cholera outbreak in Malawi. In response, the Ministry of Health implemented Oral Cholera vaccination campaigns (OCV) as one of the interventions. Four series of single-dose reactive OCV campaigns were conducted in 21 health districts between May 2022 and September 2023. OCV survey report of 2023 estimated a coverage of 55.40%. It was barely known how a single dose of OCV interrupts community transmission. This study was conducted to provide evidence on the use of a single-dose strategy and its contribution towards reducing the risk of cholera infection. Method A cross-sectional quantitative analysis was conducted to assess the effectiveness of OCV in reducing cholera incidence, severity, and mortality during the 2022-2023 cholera outbreak in Malawi. A national cholera line-list was used for analysis. Results Oral cholera vaccination coverage was at 2.0% of 28,920 suspected cholera cases. The effectiveness of a single dose of OCV towards reducing cholera infections was 98.00%. and associated with lower odds of severe dehydration (OR = 0.50; 95% CI: 0.39-0.64), with OCV effectiveness at 50%(95% CI: 36-61) Case fatality rate among vaccinated was 1.20 (95% CI: 0.54; 2.6, p = 0.025) and among unvaccinated it was 2.80% (95% CI: 2.6; 3.0, p = 0.025). Conclusion A single dose of the OCV campaign conducted during the 2022-2023 cholera outbreak in Malawi contributed to the reduction of cholera incidence. The intervention complemented other long-term interventions such as Water, Sanitation and Hygiene Oral Dehydration Points, Case Area Targeted Intervention, and Risk Communication and Community Engagements.