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Live oral cholera vaccine safe, immunogenic in adults
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Researchers from India demonstrated that a live oral recombinant cholera vaccine candidate was safe and immunogenic in adults from a cholera endemic region, according to study results published in PLOS ONE.
The randomized, double blind, placebo-controlled trial included 88 adults aged 18 to 60 years from Kolkata, India. Participants received either a lyophilized dose of the VA 1.4 cholera vaccine or placebo within 5 minutes of drinking 100 mL of a buffer solution of sodium bicarbonate and ascorbic acid. A second dose was administered on day 14. Primary endpoints were vaccine safety and immunogenicity.
The VA 1.4 vaccine was developed from a non-toxigenic Vibrio cholera 01 El Tor strain. The ctxB gene of V. cholerae, which is responsible for the production of the “B” subunit of the cholera toxin, was introduced to the strain. It is an identical construct to the VA 1.3 vaccine — which has been previously studied — with the exception that the ampicillin resistance marker tagged to the ctxB gene has been deleted.
None of the participants experienced nausea, vomiting or diarrhea, according to the researchers. Other adverse events were rare and mild, and occurred with the same frequency in both groups. The proportion of participants who seroconverted — that is, having a fourfold or higher rise in reciprocal titer — in the vaccine group were 65.9% (95% CI, 50.1-79.5) at both 7 and 21 days. None of the participants in the control group seroconverted. One participant in the vaccine group excreted the vaccine on day one but did not experience any adverse events.
Unlike its precursor, the VA 1.4 cholera vaccine did not induce good anti-cholera toxin antibody response, according to the researchers. However, anti-cholera toxin antibody titer is not regarded as a marker of protection against cholera.
No additional benefit of the vaccine was seen after two doses.
The researchers noted that an effective cholera vaccine is needed with the emergence of recent outbreaks.
“In recent years a new variant of V. cholerae El Tor emerged,” they wrote. “This variant produces cholera toxin of the type produced by the classical cholera biotype. This variant has already replaced the original El Tor strain in several parts of Asia and Africa and, appears to be associated with more severe disease. All these events therefore indicate the need for an effective single dose [of] oral vaccine for cholera to combat cholera outbreaks and it is hoped that VA 1.4 may meet this requirement.”
Disclosure: See the study for a full list of financial disclosures.
Perspective
Back to TopStephen B. Calderwood, MD
Stephen B. Calderwood
A safe, effective live oral attenuated cholera vaccine that produces durable protective immunity in all age groups after a single dose would be a valuable addition to the public health tools available for control of this serious diarrheal illness. Although there are other live oral attenuated cholera vaccines being studied, none are currently available for broad use. This study reports initial data on safety and immunogenicity in adults of a new live oral cholera vaccine produced in India, and the preliminary data are encouraging. More data on safety and immunogenicity in younger ages, as well as documentation of protective efficacy and the duration of such protection will be needed to understand whether this vaccine will be an improvement over the currently available killed oral cholera vaccines pre-approved by WHO for use in control of cholera.
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