Evaluation of Two Vaccines against Foot-and-Mouth Disease Used in Transcaucasian Countries by Small-Scale Immunogenicity Studies Conducted in Georgia, Azerbaijan and Armenia

Abstract

In countries endemic for foot-and-mouth disease (FMD), routine or emergency vaccinations are strategic tools to control the infection. According to the WOAH/FAO guidelines, a prior estimation of vaccine effectiveness is recommendable to optimize control programs. This study reports the results of a small-scale immunogenicity study performed in Transcaucasian Countries. Polyvalent vaccines, including FMDV serotypes O, A (two topotypes) and Asia1 from two different manufacturers, were evaluated in Georgia, Azerbaijan and Armenia. Naïve large and small ruminants were vaccinated once and a subgroup received a second booster dose. The titers of neutralizing antibodies in sera collected sequentially up to 180 DPV were determined through the Virus Neutralization Test versus homologous strains. This study led to the estimate that both the vaccines evaluated will not induce a protective and long-lasting population immunity, even after a second vaccination, stressing that consecutive administrations of both vaccines every three months are mandatory if one aspires to achieve protective herd immunity.

Keywords: foot-and-mouth disease; small-scale immunogenicity study; vaccination campaign; vaccine effectiveness assessment.

Figure 1

Sampling scheme. The picture represents the actual sampling carried out in the three countries, namely Georgia, Azerbaijan and Armenia. Every square corresponds to a single animal. In dark grey, the large ruminants (LR); in light grey, the small ruminants (SR). Red crosses highlight those samples that could not be analyzed because of empty vials or lost tags.

Figure 2

Immune response of large ruminants (LR) against FMDV serotype O. Charts showing the medians of log₁₀ VNT titers obtained testing the neutralizing ability of LR sera against FMDV strain O/ME-SA/PanAsia-2/TUR/07. Sera from Georgia (a), Azerbaijan (b) and Armenia (c). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log₁₀ titer in green dashed line. Empty dots and dashed red line, single-vaccinated animals (LR-01 and LR-02 before booster); filled dots and solid red line, double-vaccinated animals (LR-02 group after booster). ***, p value ≤ 0.001; *, p value ≤ 0.05.

Figure 3

Immune response of large ruminants (LR) against FMDV serotype A. Charts showing the medians of log₁₀ VNT titers obtained testing the neutralizing ability of LR sera against FMDV strain A/ASIA/Iran-05/TUR/06 (a–c) and FMDV strain A/ASIA/G-VII/NEP/84 (d–f). Sera from Georgia (a,d), Azerbaijan (b,e) and Armenia (c,f). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log10 titer in green dashed line. Empty dots and dashed blue line, single-vaccinated animals (LR-01 and LR-02 before booster); filled dots and solid blue line, double-vaccinated animals (LR-02 group after booster). ***, p value ≤ 0.001; **, p value ≤ 0.01; *, p value ≤ 0.05.

Figure 4

Immune response of large ruminants (LR) against FMDV serotype Asia1. Charts showing the median, maximum and minimum log₁₀ VNT titers obtained testing the neutralizing ability of LR sera against FMDV strain Asia1/ASIA/Sindh08/TUR/15. Sera from Georgia (a), Azerbaijan (b) and Armenia (c). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log10 titer in green dashed line. Empty dots and dashed grey line single-vaccinated animals (LR-01 and LR-02 before booster); filled dots and solid grey line, double-vaccinated animals (LR-02 group after booster). ***, p value ≤ 0.001; **, p value ≤ 0.01; *, p value ≤ 0.05.

Figure 5

Immune response of small ruminants (SR) against FMDV serotype O. Charts showing the median, maximum and minimum log₁₀ VNT titers obtained testing the neutralizing ability of SR sera against FMDV strain O/ME-SA/PanAsia-2/TUR/07. Sera from Georgia (a) and Azerbaijan (b). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log10 titer in green dashed line. Empty squares and dashed red line, single-vaccinated animals (SR-01 and SR-02 before booster); filled squares and solid red line, double-vaccinated animals (SR-02 group after booster). ***, p value ≤ 0.001; *, p value ≤ 0.05.

Figure 6

Immune response of small ruminants (SR) against FMDV serotype A. Charts showing the median, maximum and minimum log₁₀ VNT titers obtained testing the neutralizing ability of SR sera against FMDV strain A/ASIA/Iran-05/TUR/06 (a,b) and strain A/ASIA/G-VII/NEP/84 (c,d). Sera from Georgia (a,c) and Azerbaijan (b,d). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log10 titer in green dashed line. Empty squares and dashed red line, single-vaccinated animals (SR-01 and SR-02 before booster); filled squares and solid red line, double-vaccinated animals (SR-02 group after booster). *** p value ≤ 0.001; **, p value ≤ 0.01; * p value ≤ 0.05.

Figure 7

Immune response of small ruminants (SR) against FMDV serotype Asia1. Charts showing the median, maximum and minimum log₁₀ VNT titers obtained testing the neutralizing ability of SR sera against FMDV strain Asia1/ASIA/Sindh8/TUR/15. Sera from Georgia (a) and Azerbaijan (b). Abscissa, days post-vaccination (DPV); ordinate, log₁₀ VNT titers. Error bar, 95% confidence interval; VNT positivity threshold, >1.5 log10 titer in green dashed line. Empty squares and dashed grey line, single-vaccinated animals (SR-01 and SR-02 before booster); filled squares and solid grey line, double-vaccinated animals (SR-02 group after booster). **, p value ≤ 0.01; * p value ≤ 0.05 (*).

Figure 8

VNT positivity rate of vaccinated LR and SR. Charts showing the 95% confidence interval and point estimate of proportion animals with positive VNT titers against all the FMD strains included in the vaccine formula: A/ASIA/G-VII (a), A/ASIA/Iran-05 (b), Asia1/ASIA/Sindh8 (c) and O/ME-SA/PanAsia2 (d). The charts included all the ruminants and all three countries. From the top: LR from Armenia, LR from Azerbaijan, SR from Azerbaijan, LR from Georgia and SR from Georgia. Abscissa, time in days post-vaccination (DPV); ordinate, proportion of the population with VNT-positive titers (threshold of positivity > 1.5 log₁₀ titer). The green areas highlight the proportion between 0.7 and 0.8 (70–80% of animals), which is the expected VNT-positive population rate for an effective vaccination.