Cholera Vaccine: Reduction to Single Dose May Save Lives

Lara C. Pullen, PhD

August 26, 2015

Vaccination campaigns that use a single dose of oral cholera vaccine (OCV) may be able to prevent more deaths than the standard two-dose campaign, according to a modeling study published online August 25 in PLOS Medicine. Such a strategy may be especially important when vaccine supplies are limited or when an outbreak is characterized by complex logistics.

"In the midst of a rapidly growing cholera epidemic, swift action pays dividends. Our results suggest that providing a less protective single-dose OCV regimen to more people could have larger public health benefits than providing the recommended two-dose schedule to fewer people," write Andrew S. Azman, PhD, MPH, from the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, and colleagues.

The model was based on direct vaccine efficacy data, and the results were applied to recent outbreaks in Haiti, Zimbabwe, and Guinea. The investigators focused the model on minimizing the total number of cholera cases within the epidemic.

The investigators estimated that a single dose of vaccine must be 35% to 56% as efficacious as two doses for a fixed amount of vaccine to avert the same number of cases when administered at the beginning of an epidemic.

The investigators calculate that a single dose of OCV is 44% effective (95% confidence interval, −27% to 76%) compared with the 77% effectiveness observed for two doses (95% confidence interval, 57% - 88%). This difference translates into a 57% one-dose efficacy estimate, which falls above the relative single-dose efficacy of 35% to 56%.

Unfortunately, the data on the efficacy of a single dose of OCV are mixed, the authors say. They note that the uncertainty, confounds the conclusions of the study. They highlight the need for further studies to evaluate the efficacy of one-dose campaigns.

Other factors that must be considered are access, cost-effectiveness, and public perceptions of vaccine effectiveness.

"Our results contribute to a growing body of evidence, based on both empirical and computational studies, providing the basis for effective strategies for OCV use in outbreaks. We present a novel framework for weighing the public health utility of using a single dose in reactive OCV campaigns in light of current and future estimates of the efficacy of this alternative regimen. Our results highlight the trade-offs between population- and individual-level benefits of OCV dosing strategies, an important though rarely discussed topic," the authors write.

Four coauthors were supported by the Bill & Melinda Gates Foundation. One coauthor is recipient of a K22 grant from the National Institute of Allergy and Infectious Disease. The authors have disclosed no other relevant financial relationships.

PLOS Med. Published online August 25 2015. Full text

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