THE PURPOSE
Of this study is to study the effect of the dose and frequency of immunization of BALB/c mice with intradermal (i.d.) injection of the LIVP strain of vaccinia virus (VACV) on the level of their protection against the highly virulent mouse ectromelia virus (ECTV).
MATERIALS AND METHODS
Immunization of mice was carried out by i.d. injection with a single or double injection with an interval of 28 days of VACV LIVP at a dose of 105 PFU, as well as with a single injection at a dose of 106 PFU. In blood sera taken from mice during their lifetime, the dynamics of biosynthesis of VACV-specific IgG was determined by ELISA up to 140 days post vaccination (dpv). At 142 dpv, groups immunized with the LIVP virus and control animals were intranasally infected with a lethal dose of ECTV and the indicators of clinical manifestations of infection, body weight of animals and their death were monitored.
RESULTS
At 28 dpv, the level of antibodies in mice vaccinated with VACV LIVP at a dose of 106 PFU significantly exceeded the similar level in mice vaccinated with the same virus at a dose of 105 PFU. Repeated immunization with VACV LIVP at a dose of 105 PFU on 28 dpv led to a significant increase in the biosynthesis of virus-specific IgG and the level of analyzed antibodies in this group of mice corresponded to a similar indicator for the group of mice vaccinated once with VACV LIVP at a dose of 106 PFU. After infection with a lethal dose of ECTV, all animals in the control group (unvaccinated) died by the 8th day after infection, and those vaccinated with VACV LIVP once at a dose of 105 PFU died by the 14th day. In groups of mice vaccinated twice at a dose of 105 PFU and once at a dose of 106 PFU, 80% of the individuals survived.
CONCLUSION
To maintain a long-term protective immune response to vaccination with live VACV, a high dose of this virus must be used. Alternatively, a lower vaccination dose can be used, but in this case revaccination should be carried out.
