Research on post-vaccination antibody dynamics has become pivotal in estimating COVID-19 vaccine efficacy. We studied anti-SARS-CoV-2 Spike RBD IgG levels in 587 healthcare workers (2038 sera) who completed BNT162b2 vaccination. Average antibody titer 3 weeks after the first dose in COVID-19-naïve participants (median 873.5 AU/mL) was 18-fold higher than the test threshold, with a significant increase 1 month (median 9927.2 AU/mL) and an exponential decrease 3 (median 2976.7 AU/mL) and 6 (median 966.0 AU/mL) months after complete vaccination. Participants with a history of COVID-19 prior to vaccination showed significantly higher antibody levels, particularly after the first dose (median 14,280.2 AU/mL), with a slight decline 1 month (median 12,700.0 AU/mL) and an exponential decline in antibody titers 3 (median 4831.0 AU/mL) and 6 (median 1465.2 AU/mL) months after vaccination. Antibody levels of COVID-19-naïve subjects after the first dose were moderately correlated with age (r = −0.4). Multivariate analysis showed a strong independent correlation between IgG levels 6 months after vaccination and both IgG titers after the first dose and 1 month after vaccination (R2 = 0.709). Regardless of pre-vaccination COVID-19 history, IgG levels 6 months after vaccination were comparable to antibody levels reached by COVID-19-naïve participants after the first vaccine dose.

The infectious bursal disease virus (IBDv) is widespread in poultry flocks all around the world. Various biotypes have emerged and because of that, adequate management practices and vaccination of chicks are of paramount importance for the protection against field strains. One day old Lohmann Brown chicks were vaccinated with intermediate vaccines and the recombinant VAXXITEK HVT-IBDv vaccine formulation, and challenged at 48 days of life with the very virulent IBDv (vvIBDv) strain CH/99. The best protection (100%) was achieved with the recombinant vaccine administered by the subcutaneous or intramuscular route at a day old, while intermediate and intermediate plus vaccines protected 80% of birds from clinical symptoms. The highest bursa body ratio (5.33, 3.50 and 4.12) was accomplished in non- vaccinated and non-challenged birds and birds vaccinated with the VAXXITEK HVT-IBDv vaccine. The recombinant VAXXITEK HVT-IBDv vaccine has provided protection for commercial chicks against challenge with the vvIBDv strain in this experiment. Under field conditions, additional vaccination is possibly needed with supplementary application of live attenuated vaccines. However, the recombinant vector vaccines are providing significant aid against clinical signs and immunosupression caused by the vvIBDv.