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Feline calicivirus (FCV) is one of the most widespread pathogens affecting feline animals. Currently, FCV is believed to be divisible into two genotypes, with prevalent strains encompassing both GI and GII. Vaccination is the primary means of preventing FCV infection, yet traditional inactivated or attenuated vaccines theoretically pose potential safety concerns. In this study, a virus-like particles (VLPs), named DL39-VLPs, was constructed, using the VP1 gene of FCV DL39 strain with broad neutralizing and protective properties as a template through insect cell expression system. Cats were immunized with a 50 μg dose of DL39-VLPs mixed with an oily adjuvant via subcutaneous injection in the neck. For feline antisera positive for DL39-VLPs, the titer range in neutralization tests against prevalent GI strains ranged from 1:151 to 1:538, whereas the titer range in neutralization tests against prevalent GII strains was between 1:65 and 1:113. Challenge trials demonstrated that cats immunized with DL39-VLPs exhibited no significant clinical symptoms and had significantly reduced viral shedding and viremia compared to the challenged control group. Ultimately, a safe and highly protective VLP vaccine candidate, DL39-VLPs, was developed, which provides an important tool for the prevention and control of FCV infection. [ABSTRACT FROM AUTHOR]

Antigenic assessments of SARS-CoV-2 variants inform decisions to update COVID-19 vaccines. Primary infection sera are often used for assessments, but such sera are rare due to population immunity from SARS-CoV-2 infections and COVID-19 vaccinations. Here, we show that neutralization titers and breadth of matched human and hamster pre-Omicron variant primary infection sera correlate well and generate similar antigenic maps. The hamster antigenic map shows modest antigenic drift among XBB sub-lineage variants, with JN.1 and BA.4/BA.5 variants within the XBB cluster, but with fivefold to sixfold antigenic differences between these variants and XBB.1.5. Compared to sera following only ancestral or bivalent COVID-19 vaccinations, or with post-vaccination infections, XBB.1.5 booster sera had the broadest neutralization against XBB sub-lineage variants, although a fivefold titer difference was still observed between JN.1 and XBB.1.5 variants. These findings suggest that antibody coverage of antigenically divergent JN.1 could be improved with a matched vaccine antigen. IMPORTANCE Updates to COVID-19 vaccine antigens depend on assessing how much vaccine antigens differ antigenically from newer SARS-CoV-2 variants. Human sera from single variant infections are ideal for discriminating antigenic differences among variants, but such primary infection sera are now rare due to high population immunity. It remains unclear whether sera from experimentally infected animals could substitute for human sera for antigenic assessments. This report shows that neutralization titers of variant-matched human and hamster primary infection sera correlate well and recognize variants similarly, indicating that hamster sera can be a proxy for human sera for antigenic assessments. We further show that human sera following an XBB.1.5 booster vaccine broadly neutralized XBB sub-lineage variants but titers were fivef old lower against the more recent JN.1 variant. These findings support updating the current COVID-19 vaccine variant composition and developing a framework for assessing antigenic differences in future variants using hamster primary infection sera. [ABSTRACT FROM AUTHOR]

Feline calicivirus (FCV) is one of the most widespread pathogens affecting feline animals. Currently, FCV is believed to be divisible into two genotypes, with prevalent strains encompassing both GI and GII. Vaccination is the primary means of preventing FCV infection, yet traditional inactivated or attenuated vaccines theoretically pose potential safety concerns. In this study, a virus-like particles (VLPs), named DL39-VLPs, was constructed, using the VP1 gene of FCV DL39 strain with broad neutralizing and protective properties as a template through insect cell expression system. Cats were immunized with a 50 μg dose of DL39-VLPs mixed with an oily adjuvant via subcutaneous injection in the neck. For feline antisera positive for DL39-VLPs, the titer range in neutralization tests against prevalent GI strains ranged from 1:151 to 1:538, whereas the titer range in neutralization tests against prevalent GII strains was between 1:65 and 1:113. Challenge trials demonstrated that cats immunized with DL39-VLPs exhibited no significant clinical symptoms and had significantly reduced viral shedding and viremia compared to the challenged control group. Ultimately, a safe and highly protective VLP vaccine candidate, DL39-VLPs, was developed, which provides an important tool for the prevention and control of FCV infection.

The aim was to measure neutralizing antibody levels against the SARS-CoV-2 Omicron (BA.1) variant in serum samples obtained from vaccinated PLWH and healthcare workers (HCW) and compare them with those against the Wuhan-D614G (W-D614G) strain, before and after the third dose of a mRNA vaccine. We included 106 PLWH and 28 HCWs, for a total of 134 participants. Before the third dose, the proportion of participants with undetectable nAbsT against BA.1 was 88% in the PLWH low CD4 nadir group, 80% in the high nadir group and 100% in the HCW. Before the third dose, the proportion of participants with detectable nAbsT against BA.1 was 12% in the PLWH low nadir group, 20% in the high nadir group and 0% in HCW, respectively. After 2 weeks from the third dose, 89% of the PLWH in the low nadir group, 100% in the high nadir group and 96% of HCW elicited detectable nAbsT against BA.1. After the third dose, the mean log2 nAbsT against BA.1 in the HCW and PLWH with a high nadir group was lower than that seen against W-D614G (6.1 log2 (±1.8) vs. 7.9 (±1.1) and 6.4 (±1.3) vs. 8.6 (±0.8)), respectively. We found no evidence of a different level of nAbsT neutralization by BA.1 vs. W-D614G between PLWH with a high CD4 nadir and HCW (0.40 (−1.64, 2.43); p = 0.703). Interestingly, in PLWH with a low CD4 nadir, the mean log2 difference between nAbsT against BA.1 and W-D614G was smaller in those with current CD4 counts 201–500 vs. those with CD4 counts < 200 cells/mm3 (−0.80 (−1.52, −0.08); p = 0.029), suggesting that in this target population with a low CD4 nadir, current CD4 count might play a role in diversifying the level of SARS-CoV-2 neutralization. [ABSTRACT FROM AUTHOR]