Neutralizing antibody (NAb) detection is critical for evaluating herd immunity and monitoring the efficacy of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, quantitative SARS-CoV-2 antibody levels after vaccination were measured by chemiluminescent immunoassays, enzyme immunoassays, and surrogate virus neutralization tests (sVNTs), as well as plaque reduction neutralization tests (PRNT). Sequential blood samples were collected before and 1 and 3 months after vaccination in 30 healthy participants (two doses of Oxford-AstraZeneca [AZ] or Pfizer-BioNTech [BNT]). After vaccination, all sera tested positive for PRNT, with NAb titers ranging from 1:10 to 1:723. Median NAb titers were higher in the BNT vaccine group than in the AZ vaccine group at both one and three months post-vaccination. Excellent overall concordance rates were observed between serological assays and PRNT. In a quantitative correlation analysis, the results of sVNTs showed a strong correlation with those of PRNT. Results of the four binding antibody assays showed a significant correlation with those of PRNT. The serologic assays evaluated in this study could be used as sVNTs to evaluate the efficacy of SARS-CoV-2 vaccines.

The Zika virus (ZIKV) is a mosquito-borne member of the Flaviviridae family of enveloped RNA viruses. The correlation between viral infection and fetal microcephaly was revealed in 2015, yet we still lack a vaccine against ZIKV. Here, we present a genetic vaccine that delivers the premembrane (prM) and envelope (E) genes of ZIKV using a recombinant baculovirus vector that expresses a human endogenous retrovirus (HERV) envelope on its surface to enhance gene delivery. We observed that baculoviruses with HERV envelopes (AcHERV) exhibited specifically higher gene transfer efficiency in human cells compared to the wild-type baculovirus vector. Using the AcHERV baculovirus vector, we constructed a recombinant baculovirus vaccine encoding ZIKV prM/E genes (AcHERV-ZIKV), which are major targets of neutralizing antibodies. Mice immunized twice with AcHERV-ZIKV exhibited high levels of IgG, neutralizing antibodies, and IFN-γ. In challenge tests in IFN knock-out mice (A129), AcHERV-ZIKV showed complete protection in both challenge and pregnancy tests. These results suggest that AcHERV-ZIKV could be a potential vaccine candidate for human application.

The outbreak of COVID-19 has become a public health emergency of international concern; thus, it is important to not only develop drugs for treating COVID-19 but also develop a method for evaluating the therapeutic effect based on the characteristics of SARS-CoV-2 and its variants. To test the antiviral activity of a drug against COVID-19, in this study, we established and compared experimental conditions, such as the treatment time and mode of action (dose) of the therapeutic substance, and a test method to evaluate its effectiveness. We optimized an assay for testing antiviral activity by plaque reduction, tissue culture infectious dose 50, and quantitative RT-PCR. These methods were applied to test the antiviral efficacy of the therapeutic against SARS-CoV-2. Antiviral activity testing using in vitro assays against SARS-CoV-2 and its variants was assessed by measuring plaque-reducing or cytopathic effects in Vero-E6 cells. The in vitro assay was validated by evaluating the antiviral activity of remdesivir. Remdesivir reduced SARS-CoV-2 titer without detectable cytotoxicity and successfully inhibited viral replication in a dose-dependent manner. Therefore, we suggest this in vitro assay as an effective method for testing the antiviral activity for a potential repurposed drug against COVID-19 or rapid screening of therapeutic candidates.

Varicella-zoster virus (VZV) poses lifelong risks, causing varicella and herpes zoster (HZ, shingles). Currently, varicella and HZ vaccines are predominantly live attenuated vaccines or adjuvanted subunit vaccines utilizing VZV glycoprotein E (gE). Here, we propose our vaccine candidates involving a comparative analysis between recombinant baculoviral vector vaccines (AcHERV) and a live attenuated vaccine strain, vOka. AcHERV vaccine candidates were categorized into groups encoding gE only, VZV glycoprotein B (gB) only, or both gE and gB (gE-gB) as AcHERV-gE, AcHERV-gB, and AcHERV-gE-gB, respectively. Humoral immune responses were evaluated by analyzing total IgG, IgG1, IgG2a, and neutralizing antibodies. Cell-mediated immunity (CMI) responses were evaluated by enzyme-linked immunospot (ELISPOT) assay and Th1/Th2/Th17 cytokine profiling. In the mouse model, AcHERV-gE-gB elicited similar or higher total IgG, IgG2a, and neutralizing antibody levels than vOka and showed robust VZV-specific CMI responses. From the perspective of antigens encoded in vaccines and their relationship with CMI response, both AcHERV-gB and AcHERV-gE-gB demonstrated results equal to or superior to AcHERV-gE, encoding only gE. Taken together, these results suggest that AcHERV-gE-gB can be a novel candidate for alleviating risks of live attenuated vaccine-induced latency and effectively preventing varicella during early stages of life while providing strong CMI for effective resistance against HZ and therapeutic potential in later stages of life.