Evaluation of Cholera Antigen-Specific Gut-Homing β7-Positive Antibody-Secreting Cells in the Systemic Circulation of Oral Cholera Vaccinees Receiving Doses at Different Intervals

Background/Objectives: Cholera remains a significant global health challenge. Shanchol (ShantaBiotech, India), one of the WHO prequalified Oral Cholera Vaccines (OCVs) available until recently, has been used to immunize people as a two-dose regimen (14 days apart, on day 0 and 14). However, growing evidence suggests that a single-dose strategy may mediate short-term protection, especially in those over 5 years of age. Hence, it is crucial to design a suitable and effective administration scheme for Shanchol, particularly in cholera-endemic regions. Methods: In this study, adult volunteers were vaccinated with either a single dose, a two-dose regimen with a 14-day interval, or a two-dose regiment with a 30-day interval. We studied the antigen-specific helper memory (CD4+CD45RO+) and cytotoxic memory (CD8+CD45RO+) T cells responses of vaccinees along with the specific mucosal immune responses to gut-homing ß7 lipopolysaccharides (LPSs). Results: By day 7 post-vaccination, Shanchol induced robust helper and cytotoxic memory T cell responses to V. cholerae membrane protein (AKI-MP) following a single dose of vaccination. In the two-dose groups, we observed a significant elevation of AKI-MP-specific responses after the 2nd dose. We found that circulatory gut homing (β7+) LPS-specific IgA responses of antibody-secreting cells (ASCs) peaked at D7 among all vaccine groups. Moreover, we observed that β7+ LPS-specific ASCs at D7 significantly correlated with the LPS-specific antibody titer in plasma. Conclusions: These findings suggest that a single dose of OCV in adults induces immune responses comparable to a two-dose regimen, suggesting a single-dose vaccination may be adequate to mediate protection against cholera in cholera endemic zones—especially in reactive campaigns.