Oral immunization against cholera

Oral vaccines for preventing cholera

EDITORIAL NOTE

This review is superseded by the published Cochrane Review, Saif‐Ur‐Rahman 2024 [https://doi.org/10.1002/14651858.CD014573], which considers only the oral killed vaccines because the live oral vaccines do not have World Health Organization (WHO) prequalification. Saif‐Ur‐Rahman 2024 also considered only currently available WHO pre‐qualified oral killed cholera vaccines (Dukoral, Shanchol, and Euvichol/Euvichol‐Plus).

BACKGROUND

Cholera is a cause of acute watery diarrhoea which can cause dehydration and death if not adequately treated. It usually occurs in epidemics, and is associated with poverty and poor sanitation. Effective, cheap, and easy to administer vaccines could help prevent epidemics.

OBJECTIVES

To assess the effectiveness and safety of oral cholera vaccines in preventing cases of cholera and deaths from cholera.

SEARCH STRATEGY

In October 2010, we searched the Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; the metaRegister of Controlled Trials (mRCT), and the WHO International Clinical Trials Registry Platform (ICTRP) for relevant published and ongoing trials.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of oral cholera vaccines in healthy adults and children.

DATA COLLECTION AND ANALYSIS

Each trial was assessed for eligibility and risk of bias by two authors working independently. Data was extracted by two independent reviewers and analysed using the Review Manager 5 software. Outcomes are reported as vaccine protective efficacy (VE) with 95% confidence intervals (CIs).

MAIN RESULTS

Seven large efficacy trials, four small artificial challenge studies, and twenty-nine safety trials contributed data to this review.Five variations of a killed whole cell vaccine have been evaluated in large scale efficacy trials (four trials, 249935 participants). The overall vaccine efficacy during the first year was 52% (95% CI 35% to 65%), and during the second year was 62% (95% CI 51% to 62%). Protective efficacy was lower in children aged less than 5 years; 38% (95% CI 20% to 53%) compared to older children and adults; 66% (95% CI 57% to 73%).One trial of a killed whole cell vaccine amongst military recruits demonstrated 86% protective efficacy (95% CI 37% to 97%) in a small epidemic occurring within 4 weeks of the 2-dose schedule (one trial, 1426 participants). Efficacy data is not available beyond two years for the currently available vaccine formulations, but based on data from older trials is unlikely to last beyond three years.The safety data available on killed whole cell vaccines have not demonstrated any clinically significant increase in adverse events compared to placebo.Only one live attenuated vaccine has reached Phase III clinical evaluation and was not effective (one trial, 67508 participants). Two new candidate live attenuated vaccines have demonstrated clinical effectiveness in small artificial challenge studies, but are still in development.

AUTHORS' CONCLUSIONS

The currently available oral killed whole cell vaccines can prevent 50 to 60% of cholera episodes during the first two years after the primary vaccination schedule. The impact and cost-effectiveness of adopting oral cholera vaccines into the routine vaccination schedule of endemic countries will depend on the prevalence of cholera, the frequency of epidemics, and access to basic services providing rapid rehydration therapy.

Immunity to vaginal HSV-2 infection in immunoglobulin A knockout mice

An immunoglobulin A (IgA) knockout (KO) mouse was used to study the role of IgA in protective immunity against vaginal infection with herpes simplex virus-type 2 (HSV-2). Intact and KO mice were immunized intravaginally (IVAG) with attenuated HSV-2, challenged IVAG with wild-type virus 6 weeks later and evaluated for vaginal infection and neurological disease. Non-immunized/challenged intact and KO mice showed vaginal infection and succumbed to neurological disease, while immunized/challenged mice exhibited reduced or no vaginal infection and no neurological disease. Log 2.5 enzyme-linked immunoassay (ELISA) titres of viral IgA, immunoglobulin G (IgG) and immunoglobulin M (IgM) in vaginal secretions collected from intact immune mice before challenge were 0.6+/-0.3, 6.4+/-0.32 and 0.0, while those in KO immune mice were 0.0, 6.7+/-0.19 and 3.0+/-0.29, respectively. Twenty-four hours after challenge, the percentage of vaginal epithelium that was infected in non-immune intact and KO mice was 2.0+/-0.6 and 2.4+/-0.6, which was reduced to 0.2+/-0.1 and 0.1+/-0.06 in immune intact and KO mice, respectively. No shed virus protein was detected in vaginal secretions 3 days after challenge in any immune mouse, whereas titres were 1400 and 1700 in the two groups of non-immune mice. Thus, immune protection against vaginal HSV-2 infection was similar in both KO and intact mice, indicating that this mucosal immunity does not depend mainly on IgA.

Rectal immunization for induction of specific antibody in the genital tract of women

The purpose of the current study was to examine potential routes of vaccine administration for the induction of antigen-specific responses in the genital tract of women. Sixteen women were enrolled in this study, and the level of influenza-specific antibodies induced in the genital tract was measured after rectal or intramuscular immunizations. Both methods of administration induced significant increases in the concentration of flu-specific IgA found in cervical secretions within 28 days after vaccination. Initially flu-specific IgG antibodies were not induced in the genital tract by either route. As expected both IgA and IgG flu-specific antibodies were dramatically increased in serum after intramuscular vaccination. In contrast, rectal administration did not induce significant IgA responses, and only small flu-specific IgG increases in serum. Six months after administration, IgA flu-specific antibody concentrations were significantly higher than baseline levels in vaginal secretions and saliva isolated from both subject groups and flu-specific IgG concentrations in cervical secretions were high in the rectal immunization group. The long-term presence of both IgG and IgA antibody in genital secretions suggests that rectal immunization may be an effective method for induction of immune protection in the genital tract of women.