Two-dose killed whole-cell oral cholera vaccines are significantly less effective for children younger than 5 years than for those 5 years and older, with protection lasting for at least 3 years, according to a study published in The Lancet Infectious Diseases.
“Killed whole-cell oral cholera vaccines (kOCVs) are now becoming part of the standard cholera control and prevention toolkit, in addition to the established water sanitation, hygiene interventions, surveillance and case management,” Qifang Bi, MHS, from the Johns Hopkins Bloomberg School of Public Health, and colleagues wrote. “Although kOCVs have been used across multiple settings and have been shown to be safe and immunogenic, effectiveness and efficacy studies have provided a wide range of effect estimates, hindering clear communication to policymakers and clinicians.”
To estimate the short- and long-term efficacy of kOCVs, the researchers conducted a systematic review and meta-analysis of literature regarding randomized control trials and observational studies gathered from PubMed, Embase, Scopus, the Cochrane Review Library and the ISI Web of Science. The literature included was written in English, Spanish, French and Chinese, and contained information on estimates of cholera that was prevented by vaccination. Efficacy in relation to vaccine doses, duration and age group was also analyzed.
The researchers included seven trials (695 participants) and six observational studies (217 participants) in their review. Efficacy was observed at 58% with two doses (95% CI, 42%-69%; I2=58%) and an overall effectiveness of 76% (62%-85%; I2 = 0). Two-dose kOCVs had an efficacy of 30% in children younger than 5 years (95% CI, 15%-42%) compared with 64% in children 5 years and older (58%-70%, I2= 0%; P <.0001).
Similar efficacy estimates were noted within the first 2 years after vaccination for two doses of kOCVs, with 56% efficacy observed within the first year (95% CI, 42%-66%, I2 = 45%) and 59% within the second (49%-67%, I2 = 0). By the third year, this percentage falls to 39% (13%-57%, I2 = 48%) and 26% by the fourth year (–46% to 63%, I2 = 4%).
“The choice of using a one-dose or two-dose regimen is difficult, particularly during outbreaks in regions where supplies are scarce,” Bi and colleagues wrote. “Our estimates of the short-term — up to 1 year after vaccination — one-dose and two-dose effectiveness are similar; however, this comparison was not possible for efficacy studies because of scarce data.” – by Katherine Bortz
Disclosure: Pezzoli, Ivers, Sack, Lessler and Azman report grants from the Bill & Melinda Gates Foundation. Bi, Ferreras, Date Qadri, Digilio, Ali and Luqero declare no competing interests.