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Single dose of oral cholera vaccine less effective in younger children
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Recent findings showed that a single dose of oral cholera vaccine was 40% effective for individuals aged 5 years and older in Bangladesh, although its efficacy declined to 16% in younger children.
“Our findings indicate that a single dose of the killed oral cholera vaccine provided 40% protection against all cholera for at least 6 months of follow-up in a population living in an area in which cholera was highly endemic,” Firdausi Qadri, PhD, director at the Center for Vaccine Sciences, International Center for Diarrheal Disease and Research in Bangladesh, and colleagues wrote. “From a pragmatic perspective, our data suggest that a single dose of vaccine will not be adequate for young children who are targeted for vaccination in settings in which cholera is endemic.”
In a previous trial conducted in Bangladesh, the currently recommended inactivated two-dose cholera vaccine demonstrated 53% efficacy after 2 years of follow-up, the researchers wrote. To provide a quicker and cheaper alternative for a potential epidemic, Qadri and colleagues sought to determine if a single dose also would be effective.
In their study, the researchers assessed 204,700 participants aged 1 year or older, who were randomly assigned to a single dose of oral, inactivated cholera vaccine or placebo during January and February 2014. Between 7 and 180 days after vaccine administration, the researchers examined each participant for regular or severely dehydrating culture-confirmed cholera. In addition, Qadri and colleagues compared the results between the first 83 days and last 90 days, and they analyzed the outcomes among different age groups.
They found that the overall efficacy was 40% (95% CI, 11-60) and that the efficacy against severely dehydrating cholera was 63% (95% CI, 24-82). Among participants aged 1 to 4 years, however, the vaccine was only 16% effective (95% CI, –49 to 53). In the group aged 5 to 14 years, the vaccine was 63% effective (95% CI, –39 to 90). And in the group aged 15 years and older, the effectiveness was 56% (95% CI, 16-77). Overall, adverse events were similar between the vaccine and placebo groups.
“Because a single dose of this vaccine seems sufficient at least for short-term protection of older children and adults, infrastructural changes to completing a two-dose regimen need not be a consideration in the decision to use the vaccine to help contain epidemics in these settings,” Qadri and colleagues wrote. “Similarly, our findings provide further encouragement for the use of a two-dose regimen for the routine control of endemic cholera, because some degree of protection will be provided to older children and adults who do not receive a second dose.” – by Will Offit
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Jon Andrus, MD
Cholera is a scourge that has causes devastating health consequences, particularly in impoverished communities where outbreaks are most likely to occur. In response to cholera outbreaks in developing countries, historically multi-dose vaccines often presented daunting challenges to the responders, particularly for ensuring second doses are administered in a timely fashion to individuals who received the first dose. Having a single dose vaccine intervention is a tremendous boost for future cholera prevention and control efforts. Regardless, efforts to continue to provide safe water and sanitation will also need priority support in resource-poor settings.
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