Understanding the long-term dynamics of SARS-CoV-2 neutralizing antibodies is critical for evaluating vaccine-induced protection and informing booster strategies. In this longitudinal study, we analyzed 114 serum samples from 19 individuals across six time points over a three-year period following mRNA vaccination (Comirnaty) and natural SARS-CoV-2 infection. Using pseudotype-based neutralization assays against nine SARS-CoV-2 variants, including major Omicron subvariants (BA.1–BA.5, BQ.1.1, XBB), and anti-S1 IgG ELISA, we observed that antibody levels peaked after the third vaccine dose and remained relatively stable two years later. Neutralization titers rose markedly after the second and third doses, with the highest neutralization observed at two years post-booster. Strong correlations were found between anti-S1 IgG levels and mean neutralization titers for pre-Omicron variants (r = 0.79–0.93; p < 0.05), but only moderate for Omicron subvariants (r ≈ 0.50–0.64). Notably, hybrid immunity (vaccination plus infection) resulted in higher neutralization titers at the final time point compared to vaccine-only participants. The lowest neutralization was observed against XBB, underscoring the immune evasiveness of emerging variants. These findings support the importance of booster vaccination and highlight the added durability of hybrid immunity in long-term protection.

The tick-borne encephalitis virus (TBEV) is an important human pathogen that causes tick-borne encephalitis, a potentially fatal neurological disease. Human infections occur through tick bites or after the consumption of raw milk products from infected animals, causing alimentary outbreaks representing a significant public health problem in Slovakia. In the present study, a total of 1029 ruminant sera (from 672 sheep and 357 goats) from 18 localities, collected in Slovakia during 2017-2019 were initially screened for TBEV-specific antibodies by ELISA, and 98 (9.5 %) of them were confirmed as positive by the plaque reduction neutralization test or immunofluorescence assay. The differences in observed seroprevalence of 11.9 % (80/672) among sheep and of 5.0 % (18/357) among goats were significant. Tick screening was subsequently conducted near the surveyed farms where seropositive animals were identified. Overall, 2,534 ticks (2,528 Ixodes ricinus, 3 Dermacentor reticulatus, 2 Dermacentor marginatus, 1 Haemaphysalis concinna) from 7 collection sites were pooled and analysed by RT-qPCR, resulting in estimated prevalence of 2.86 % (ranging from 0.31 to 8.72 % at different sites). The estimated prevalence in adults was lower (2.15 %) than in nymphs (2.9 %). Positive ticks (all I. ricinus) and milk samples were then used for virus isolation. Three new cell culture isolates were prepared and sequenced. Obtained full-length genome sequences revealed high genetic diversity and phylogenetic clustering with virus strains found across Europe. The seroprevalence of TBEV in farm animals is an effective tool for identifying areas of virus circulation and guiding more in-depth field investigations of local tick populations. This combined approach of serological and virological surveillance provides valuable data for assessing the risk of alimentary TBEV infections and characterizing local TBEV strains.

Understanding the long-term dynamics of SARS-CoV-2 neutralizing antibodies is critical for evaluating vaccine-induced protection and informing booster strategies. In this longitudinal study, we analyzed 114 serum samples from 19 individuals across six time points over a three-year period following mRNA vaccination (Comirnaty) and natural SARS-CoV-2 infection. Using pseudotype-based neutralization assays against nine SARS-CoV-2 variants, including major Omicron subvariants (BA.1–BA.5, BQ.1.1, XBB), and anti-S1 IgG ELISA, we observed that antibody levels peaked after the third vaccine dose (mean ELISA ratio ± SD: 8.89 ± 1.65 S/C) and remained relatively stable two years later (mean: 7.53± 1.17 S/C). Neutralization titers rose markedly after the second and third doses, with the highest neutralization observed at two years post-booster. Strong correlations were found between anti-S1 IgG levels and mean neutralization titers for pre-Omicron variants (r = 0.79–0.93; p<0.05), but only moderate for Omicron subvariants (r ≈ 0.50–0.64). Notably, hybrid immunity (vaccination plus infection) resulted in higher neutralization titers at the final time point compared to vaccine-only participants. The lowest neutralization was observed against XBB, underscoring the immune evasiveness of emerging variants. These findings support the importance of booster vaccination and highlight the added durability of hybrid immunity in long-term protection.