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

• Published in: Clinical and experimental vaccine research (Seoul) Vol. 7; no. 2; pp. 104 - 110
• Main Authors: Lee, Eun Young, Lee, Sena, Rho, Semi, Kim, Jae-Ouk, Choi, Seuk Keun, Lee, Young Jin, Park, Joo Young, Song, Manki, Yang, Jae Seung
• Format: Journal Article
• Language: English
• Published: Korea (South) Korean Vaccine Society 01.07.2018; The Korean Vaccine Society; 대한백신학회
• Subjects: Antibodies; Cholera; Enzymes; Infections; Original; Public health; Statistical analysis; Vaccines; 예방의학; United States > US; Cholera vaccines; Thimerosal; Animal models; Vaccine immunogenicity
• ISSN: 2287-3651; 2287-366X
• DOI: 10.7774/cevr.2018.7.2.104

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. 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 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. 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 challenge but not oral immunization. There was no significant difference in protection between two Euvichol variations. 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 the potency of OCVs.