Effectiveness of oral cholera vaccine in preventing cholera among fishermen in Lake Chilwa, Malawi: A case-control study.

Wednesday 19 June 2019

Grandesso F Kasambara W Page AL Debes AK M'bang'ombe M Palomares A Lechevalier P Pezzoli L Alley I Salumu L Msyamboza K Sack D Cohuet S Luquero FJ

Vaccine 2019 Jun 19; 37(28); 3668-3676. doi: 10.1016/j.vaccine.2019.05.044. Epub 2019 05 24

Cholera Effectiveness Hard-to-reach populations Malawi Thermostability Vaccine

Abstract

BACKGROUND: In response to a cholera outbreak among mobile, difficult-to-reach fishermen on Lake Chilwa, Malawi in 2016, a novel vaccine distribution strategy exploited the proven vaccine thermostability. Fishermen, while taking the first vaccine dose under supervision, received the second dose in a sealed bag, and were told to drink it two weeks later. This study assessed short-term vaccine protection of this strategy.

METHODS: Patients with diarrhoea admitted to health facilities around lake were interviewed and a stool sample collected for PCR testing. Vaccine effectiveness was assessed in a case-control test-negative design by comparing cases (PCR-positive for V. cholerae O1) and controls (patients with diarrhoea but PCR-negative) and with the screening method that compared the proportions of vaccinated among cholera cases versus the general fishermen population.

RESULTS: Of 145 study participants, 120 were fishermen living on the lake. Vaccine effectiveness at three-months was 90.0% [95%CI:38.8;98.4] among fishermen and 83.3% [95%CI: 20.8; 96.5] among all participants in the case-control test-negative design, and 97.5% [95%CI: 90.9;99.3] with the screening method.

CONCLUSION: This strategy was effective in providing short-term protection in fishermen against cholera. Further research is needed to determine the adding value of the second dose and to identify the optimal vaccination strategies for different contexts.

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