Clin Exp Vaccine Res.  2018 Jul;7(2):104-110. 10.7774/cevr.2018.7.2.104.

Immunogenicity of a bivalent killed thimerosal-free oral cholera vaccine, Euvichol, in an animal model

• Lee EY
• Lee S
• Rho S
• Kim JO
• Choi SK
• Lee YJ
• Park JY
• Song M
• Yang JS

• KMID: 2418088
• DOI: http://doi.org/10.7774/cevr.2018.7.2.104

Abstract

PURPOSE
An oral cholera vaccine (OCV), Euvichol, with thimerosal (TM) as preservative, was prequalified by the World Health Organization (WHO) in 2015. In recent years, public health services and regulatory bodies recommended to eliminate TM in vaccines due to theoretical safety concerns. In this study, we examined whether TM-free Euvichol induces comparable immunogenicity to its TM-containing formulation in animal model.
MATERIALS AND METHODS
To evaluate and compare the immunogenicity of the two variations of OCV, mice were immunized with TM-free or TM-containing Euvichol twice at 2-week interval by intranasal or oral route. One week after the last immunization, mice were challenged with Vibrio cholerae O1 and daily monitored to examine the protective immunity against cholera infection. In addition, serum samples were obtained from mice to measure vibriocidal activity and vaccine-specific IgG, IgM, and IgA antibodies using vibriocidal assay and enzyme-linked immunosorbent assay, respectively.
RESULTS
No significant difference in immunogenicity, including vibriocidal activity and vaccine-specific IgG, IgM, and IgA in serum, was observed between mice groups administered with TM-free and -containing Euvichol, regardless of immunization route. However, intranasally immunized mice elicited higher levels of serum antibodies than those immunized via oral route. Moreover, intranasal immunization completely protected mice against V. cholerae challenge but not oral immunization. There was no significant difference in protection between two Euvichol variations.
CONCLUSION
These results suggested that TM-free Euvichol could provide comparable immunogenicity to the WHO prequalified Euvichol containing TM as it was later confirmed in a clinical study. The pulmonary mouse cholera model can be considered useful to examine in vivo the potency of OCVs.

Keyword

Thimerosal; Cholera vaccines; Vaccine immunogenicity; Animal models

MeSH Terms

Animals*
Antibodies
Cholera Vaccines
Cholera*
Clinical Study
Enzyme-Linked Immunosorbent Assay
Immunization
Immunoglobulin A
Immunoglobulin G
Immunoglobulin M
Mice
Models, Animal*
Public Health
Thimerosal
Vaccines
Vibrio cholerae O1
World Health Organization
Antibodies
Cholera Vaccines
Immunoglobulin A
Immunoglobulin G
Immunoglobulin M
Thimerosal
Vaccines

Figure

• 

  Fig. 1 Intranasal immunization with thimerosal (TM)-free and -containing Euvichol protects mice against a challenge with Vibrio cholerae O1 Inaba. Four groups of mice (n=10-12) were administered intranasally or orally with TM-containing or -free Euvichol on day 0 and day 14 against a control group of non-immunized mice. Survival rate (A) and percentage weight change (B) were daily monitored following challenge with a lethal dose of V. cholerae O1 Inaba. i.n., intranasal; TM(+), thimerosal-containing; TM(−), thimerosal free.

• 

  Fig. 2 Intranasal immunization with thimerosal-free and -containing Euvichol induces vibriocidal antibody response to Vibrio cholerae. Four groups of mice (n=10-12) were administered intranasally or orally with TM-containing or -free Euvichol on day 0 and day 14 against a control group of non-immunized mice. Serum samples were collected from non-immunized and immunized mice groups on day 21 and vibriocidal activities were measured. Data represent mean values±standard error of mean from triplicate assays. *p<0.05 indicates statistically significant difference between two experimental groups by use of one-way ANOVA with Tukey's multiple comparison test. n.s, not significant; i.n., intranasal; TM(+), thimerosal-containing; TM(−), thimerosal free.

• 

  Fig. 3 Intranasal immunization with thimerosal-free and -containing Euvichol induces Vibrio cholerae-specific antibody responses. Four groups of mice (n=10-12) were administered intranasally or orally with TM-containing or -free Euvichol on day 0 and day 14 against a control group of non-immunized mice. Serum samples were obtained at 1 week after the last immunization, and V. cholerae-specific IgG (A), IgM (B), and IgA (C) titers were measured. Data represent mean values±standard error of mean from triplicate assays. *p<0.05 indicates statistically significant difference between two experimental groups by use of one-way ANOVA with Tukey's multiple comparison test. n.s, not significant; i.n., intranasal; TM(+), thimerosal-containing; TM(−), thimerosal free.

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