Antibody Persistence and Safety through 6 Months after Heterologous Orally Aerosolised Ad5-nCoV in individuals primed with two-dose CoronaVac previously (preprint)

Background: Heterologous orally administered adenovirus type-5 vector-based COVID-19 vaccine (Ad5-nCoV) in individuals who were primed with two-dose CoronaVac (an inactivated SARS-CoV-2 vaccine, by Sinovac) previously, has been reported to be safe and highly immunogenic within 28 days post-boosting. However, antibody persistence and safety up to 6 months of this regimen are not been reported yet. Methods: This is a randomized, open label, single-center trial on safety and immunogenicity of heterologous boost immunization with an orally administered aerosolised Ad5-nCoV vs. homologous boost immunization with CoronaVac after two-dose priming with CoronaVac in Chinese adults aged 18 years and older (NCT05043259). We followed the participants in this trial, including 140 in the low-dose aerosolised Ad5-nCoV group, 139 in the high-dose aerosolised Ad5-nCoV group, and 140 in the CoronaVac group for 6 months. Neutralising antibodies (NAbs) against live wild-type SARS-CoV-2 virus and omicron variant, and receptor-binding domain (RBD)-specific IgG antibodies were detected in serum samples collected at 28 days, 3 months, and 6 months after the booster dose. Serious adverse events (SAEs) were documented till month 6. Results: The low-dose and high-dose heterologous boost immunisation groups had NAb GMTs against live wild-type SARS-CoV-2 of 1937.3 [95% CI 1466.9, 2558.4] and 1350.8 [95% CI 952.6, 1915.3], which were 26.4 folds and 18.4 folds higher than that the CoronaVac group did (73.5 [95%CI 52.3, 103.3]) at 28 days. The low-dose and high-dose heterologous boost immunisation groups had NAb GMTs against live wild-type SARS-CoV-2 of 530.1 (95% CI 412.5, 681.1) and 457.6 (95%CI 349.4, 599.2), which were 26.0 folds and 22.4 folds higher than that the CoronaVac group did (20.4 [95%CI 14.3, 29.1]) at 3 months, respectively. At 6 months, the low-dose and high-dose heterologous booster groups had NAb GMTs against live wild-type SARS-CoV-2 of 312.9 (95%CI 237.7, 411.8) and 251.1 (95%CI 178.2, 354.0), which were 30.1 folds and 24.1 folds higher than the CoronaVac group did (10.4 [95%CI 7.8, 14.0]), respectively. Additionally, the low-dose and high-dose heterologous booster groups had NAb GMTs against live omicron variant of 52.0 (95%CI 37.2, 72.6) and 23.1 (95%CI 15.7, 33.9) at 28 days, 27.9 (95% CI 18.8, 41.3) and 23.3 (95%CI 16.2, 33.3) at 3 months, 16.0 (95%CI 10.9, 23.5) and 12.0 (95%CI 8.5, 16.8) at 6 months, respectively. However, nearly all participants had no detectable NAbs for omicron variant in the CoronaVac group at either 28 days, 3 months, or 6 months. No vaccine-related SAEs were observed. Conclusions: These data suggested that heterologous aerosolised Ad5-nCoV following two-dose CoronaVac priming was safe and persistently more immunogenic than three-dose CoronaVac, although immune responses waned over time.

Safety and immunogenicity of heterologous boost immunization with an adenovirus type-5-vectored and protein-subunit-based COVID-19 vaccine (Convidecia/ZF2001): a randomized, observer-blinded, placebo-controlled trial (preprint)

Background Heterologous boost vaccination has been proposed as an option to elicit stronger and broader, or longer-lasting immunity. We assessed the safety and immunogenicity of heterologous immunization with a recombinant adenovirus type-5-vectored COVID-19 vaccine (Convidecia) and a protein-subunit-based COVID-19 vaccine (ZF2001). Methods and Findings We did a randomized, observer-blinded, placebo-controlled trial in healthy adults previously received one dose of Convidecia. Participants were randomly assigned (2:1) to receive either ZF2001 (vaccine group) or a trivalent inactivated influenza vaccine (TIV) (placebo group) at either 28-day or 56-day intervals. For both regimens, all participants received the 2nd injection with ZF2001 at 4 months after a dose of ZF2001 or TIV, with three-dose schedules of Convidecia/Convidecia/ZF2001 at day 0, day 28 and month 5 (referred to as CV/ZF/ZF (D0-D28-M5)) and CV/ZF/ZF (D0-D56-M6), and two-dose schedules of CV/ZF (D0-M5) and CV/ZF (D0-M6). The primary outcome was the geometric mean titer (GMT) of the neutralizing antibodies against live SARS-CoV-2 virus 14 days after each boost vaccination. The safety outcome was 7-day reactogenicity, measured as solicited local or systemic adverse reactions after each vaccination. Between April 7, 2021, and May 6, 2021, 120 participants were enrolled, among whom 60 were randomly assigned to receive ZF2001 (n=40) or TIV (n=20) at a 28-day interval, and 60 were randomly assigned to receive ZF2001 (n=40) or TIV (n=20) at a 56-day interval. 113 (94.2%) participants received the 2nd injection with ZF2001 4 months after a dose of ZF2001 or TIV. A total of 26 participants (21.7%) reported solicited adverse events within 7 days post boost vaccinations, and all the reported adverse reactions were mild . Among participants receiving ZF001 as second dose, the GMTs of neutralizing antibodies increased to 58.4 IU/ml (42.8-79.8) in 0-28 regimen, and to 80.8 IU/ml (53.1-122.9) in 0-56 regimen at 14 days post first boost dose. The GMTs of neutralizing antibodies increased to 334.9 IU/ml (95% CI 230.4, 486.9) in C/Z/Z (D0-D28-M5) regimen, and 441.2 IU/ml (260.8, 746.4) in C/Z/Z (D0-D56-M6) regimen at 14 days after the third dose. Two-dose schedules of CV/ZF (D0-M5) and CV/ZF (D0-M6) induced comparable antibody level comparable with that elicited by three-dose schedules, with the GMTs of 282.9 IU/ml (142.5, 561.8) and 293.9 IU/ml (137.6, 627.9), respectively. Study limitations include the absence of vaccine effectiveness in real-world, and current lack of immune persistence data and the neutralizing antibodies to Omicron. Conclusions Heterologous boosting with ZF001 following primary vaccination of Convidecia is safe and more immunogenic than a single dose of Convidecia. These results support flexibility in cooperating viral vectored vaccines and recombinant protein vaccine. Trial Registration ClinicalTrial.gov NCT04833101

A trimeric NTD and RBD SARS-CoV-2 subunit vaccine induced protective immunity in CAG-hACE2 transgenic mice and rhesus macaques (preprint)

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to significant public health, economic and social problems. Development of effective vaccines is still a priority to contain the virus and end the global pandemic. In this study, we reported that ReCOV, a recombinant trimeric NTD and RBD two-component SARS-CoV-2 subunit vaccine adjuvanted with BFA03 (an AS03-like squalene adjuvant), induced high levels of neutralizing antibodies against SARS-CoV-2 and the circulating variants in mice, rabbits and rhesus macaques. Notably, two-dose immunizations of ReCOV provided complete protection against challenge with SARS-CoV-2 in hACE2 transgenic mice and rhesus macaques, without observable antibody-dependent enhancement of infection. These results support further clinical development of ReCOV and the vaccine is currently being evaluated in a phase I clinical trial in New Zealand ( NCT04818801 ).

Previously unrecognized non-reproducible antibody-antigen interactions and their implications for diagnosis of viral infections including COVID-19 (preprint)

Antibody-antigen (Ab-Ag) interactions are canonically described by a model which exclusively accommodates non-interaction (0) or reproducible-interaction (RI) states, yet this model is inadequate to explain often-encountered non-reproducible signals. Here, by monitoring diverse experimental systems and confirmed COVID-19 clinical sera using a peptide microarray, we observed that non-specific interactions (NSI) comprise a substantial proportion of non-reproducible antibody-based results. This enabled our discovery and capacity to reliably identify non-reproducible Ab-Ag interactions (NRI), as well as our development of a powerful explanatory model ("0-RI-NRI-Hook four-state model") that is [mAb]-dependent, regardless of specificity, which ultimately shows that both NSI and NRI are not predictable yet certain-to-happen. In experiments using seven FDA-approved mAb drugs, we demonstrated the use of NSI counts in predicting epitope type. Beyond challenging the centrality of Ab-Ag interaction specificity data in serology and immunology, our discoveries also facilitated the rapid development of a serological test with uniquely informative COVID-19 diagnosis performance.

Immunogenicity and Safety of a SARS-CoV-2 Inactivated Vaccine (KCONVAC) in Healthy Adults: Two Randomized, Double-blind, and Placebo-controlled Phase 1/2 Clinical Trials (preprint)

Background The significant morbidity and mortality resulted from the infection of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) call for urgent development of effective and safe vaccines. We report the immunogenicity and safety of a SARS-CoV-2 inactivated vaccine, KCONVAC, in healthy adults. Methods Two phase 1 and phase 2 randomized, double-blind, and placebo-controlled trials of KCONVAC were conducted in Chinese healthy adults aged 18 through 59 years. The phase 1 trial was conducted in a manner of dosage escalation. The first 30 participants were randomized in a ratio of 4:1 to receive two doses of either KCONVAC at 5 g per dose or placebo on Day 0 and Day 14, and the second 30 participants were randomized to receive either KCONVAC at 10 g per dose or placebo following the same procedures. The participants in the phase 2 trial were randomized in a ratio of 2:2:1 to receive either KCONVAC at 5 g or 10 g per dose, or placebo on Day 0 and Day 14, or Day 0 and Day 28. In the phase 1 trial, the primary safety endpoint was the proportion of participants experiencing adverse reactions/events within 28 days following each vaccination. Antibody response and cellular response were assayed in the phase 1 trial. In the phase 2 trial, the primary immunogenicity endpoint was the seroconversion and titre of neutralization antibody, and the seroconversion of receptor binding domain (RBD)-IgG 28 days after the second dose. Findings In the phase 1 trial, 60 participants were enrolled and received at least one dose of 5-g vaccine (N=24), 10-g vaccine (N=24), or placebo (N=12). In the phase 2 trial, 500 participants were enrolled and received at least one dose of 5-g vaccine (N=100 for 0/14 or 0/28 regimens), 10-g vaccine (N=100 for each regimen), or placebo (N=50 for each regimen). In the phase 1 trial, 13 (54%), 11(46%), and 7 (58%) participants reported at least one adverse event (AE), of whom 10 (42%), 6 (25%), and 6 (50%) participants reported at least one vaccination-related AE after receiving 5-g vaccine, 10-g vaccine, or placebo, respectively. In the phase 2 trial, 16 (16%), 19 (19%), and 9 (18%) participants reported at least one AE, of whom 13 (13%), 17 (17%), and 6 (12%) participants reported at least one vaccination-related AE after receiving 5-g vaccine, 10-g vaccine, or placebo at the regimen of Day 0/14, respectively. Similar results were observed in the three treatment groups of Day 0/28 regimen. All the AEs were grade 1 or 2 in intensity. No AE of grade 3 or more was reported. One SAE (foot fracture) was reported in the phase 1 trial. KCONVAC induced significant antibody response. 87.5% (21/24) to 100% (24/24) of participants in the phase 1 trial and 83.0% (83/100) to 100% (99/99) of participants in the phase 2 trial seroconverted for neutralising antibody to live virus, neutralising antibody to pseudovirus, and RBD-IgG after receiving two doses. Across the treatment groups in the two trials, the geometric mean titres (GMTs) of neutralising antibody to live virus ranged from 29.3 to 49.1 at Day 0/14 regimen and from 100.2 to 131.7 at Day 0/28 regimen, neutralising antibody to pseudovirus ranged from 69.4 to 118.7 at Day 0/14 regimen and from 153.6 to 276.6 at Day 0/28 regimen, and RBD-IgG ranged from 605.3 to 1169.8 at Day 0/14 regimen and from 1496.8 to 2485.5 at Day 0/28 regimen. RBD-IgG subtyping assay showed that a significant part of RBD-IgG was IgG1. The vaccine induced obvious T-cell response with 56.5% (13/23) and 62.5% (15/24) of participants in 5-g and 10-g vaccine groups showed positive interferon-{gamma} enzyme-linked immunospot responses 14 days after the second dose in the phase 1 trial, respectively. Interpretation KCONVAC is well tolerated and able to induce robust antibody response and cellular response in adults aged 18 to 59 years, which warrants further evaluation with this vaccine in the upcoming phase 3 efficacy trial. Funding Guandong Emergency Program for Prevention and Control of COVID-19 (2020A1111340002) and Shenzhen Key Research Project for Prevention and Control of COVID-19.

A proof of concept for neutralizing antibody-guided vaccine design against SARS-CoV-2 (preprint)

Mutations and transient conformational movements of receptor binding domain (RBD) that make neutralizing epitopes momentarily unavailable, present immune escape routes to SARS-CoV-2. To mitigate viral escape, we developed a cocktail of neutralizing antibodies (NAbs) targeting epitopes located on different domains of spike (S) protein. Screening of a library of monoclonal antibodies generated from peripheral blood mononuclear cells of COVID-19 convalescent patients yielded potent NAbs, targeting N-terminal domain (NTD) and RBD domain of S, effective at nM concentrations. Remarkably, combination of RBD-targeting NAbs and NTD-binding NAb, FC05, dramatically enhanced the neutralization potency in cell-based assays and animal model. Results of competitive SPR assays and cryo-EM structures of Fabs bound to S unveil determinants of immunogenicity. Combinations of immunogens, identified in NTD and RBD of S, when immunized in rabbits elicited potent protective immune responses against SARS-CoV-2. These results provide a proof-of-concept for neutralization-based immunogen design targeting SARS-CoV-2 NTD and RBD.

Immunogenicity and Safety of a SARS-CoV-2 Inactivated Vaccine in Healthy Adults Aged 18-59 years: Report of the Randomized, Double-blind, and Placebo-controlled Phase 2 Clinical Trial (preprint)

BACKGROUND The top priority for the control of COVID-19 pandemic currently is the development of a vaccine. A phase 2 trial conducted to further evaluate the immunogenicity and safety of a SARS-CoV-2 inactivated vaccine (CoronaVac). METHODS We conducted a randomized, double-blind, placebo-controlled trial to evaluate the optimal dose, immunogenicity and safety of the CoronaVac. A total of 600 healthy adults aged 18-59 years were randomly assigned to receive 2 injections of the trial vaccine at a dose of 3 g/0.5 mL or 6 g /0.5mL, or placebo on Day 0,14 schedule or Day 0,28 schedule. For safety evaluation, solicited and unsolicited adverse events were collected after each vaccination within 7 days and 28 days, respectively. Blood samples were taken for antibody assay. RESULTS CoronaVac was well tolerated, and no dose-related safety concerns were observed. Most of the adverse reactions fell in the solicited category and were mild in severity. Pain at injection site was the most frequently reported symptoms. No Grade 3 adverse reaction or vaccine related SAEs were reported. CoronaVac showed good immunogenicity with the lower 3 g dose eliciting 92.4% seroconversion under Day 0,14 schedule and 97.4% under Day 0,28 schedule. 28 days after two-dose vaccination, the Nab levels of individual schedules range from 23.8 to 65.4 among different dosage and vaccination schedules. CONCLUSIONS Favorable safety and immunogenicity of CoronaVac was demonstrated on both schedules and both dosages, which support the conduction of phase 3 trial with optimum schedule/dosage per different scenarios.

Safety, Tolerability and Immunogenicity of a Recombinant Adenovirus Type 5 Vectored COVID-19 Vaccine in Healthy Adults in China: Preliminary Report of a First-In Human Single-Center, Open-Label, Dose-Escalating Clinical Trial (preprint)

Background: We aimed to assess the safety, tolerability and immunogenicity of a recombinant adenovirus type 5 (Ad5) vectored COVID-19 vaccine expressing the spike glycoprotein of a SARS-Cov-2 strain. This is the first-in-human study of a candidate vaccine against COVID-19.Methods: We conducted a single-center, open-label, dose-escalating clinical trial of Ad5 vectored COVID-19 vaccine. Healthy adults aged between 18-60 years were sequentially enrolled and allocated to receive a single intramuscular injection in one of three dose groups: 5 × 10^10, 1×10^11, and 1·5×10^11 viral particles. Safety was assessed over the next 28 days. Specific antibodies were measured on enzyme-linked immunosorbent assay (ELISA), and the neutralizing antibody responses induced by vaccination were detected by using SARS-CoV-2 virus neutralization and pseudovirus neutralization tests. T-cell responses were accessed by enzyme-linked immunospot (ELISpot) and flow-cytometry assays. Results: A total of 108 participants were recruited and received low dose, middle dose, or high dose vaccine, with 36 in each dose group. 30(83·3%), 30(83·3%), and 27(75·0%) recipients in the low dose, middle dose, and high dose groups reported at least one adverse reaction within the first 7 days after the vaccination. The most common injection-site adverse reaction was pain, the most commonly reported systematic adverse reactions were fever, fatigue, headache, and muscle pain. A majority of the adverse reactions that were reported in all dose groups were mild or moderate in severity. No serious adverse event was noted within 28 days post-vaccination. Both ELISA antibodies and neutralizing antibodies increased significantly at day 14, and peaked 28 days post-vaccination. Specific T cell response peaked at day 14 post-vaccination.Conclusions: The Ad5 vectored COVID-19 vaccine is tolerable and immunogenic. Humoral responses against SARS-CoV-2 peaked at day 28 post-vaccination in health adults, and rapid specific T cell responses were noted since day 14.Trial Registration: The study is registered with ClinicalTrials.gov, number NCT04313127. Funding Statement: National Key R&D Program of China (2020YFC10841400), National Science and Technology Major Project (2016ZX10004001, 2018ZX09201005), and CanSino Biotechnology Inc.Declaration of Interests: Mr. Gou report being employees of Tianjin CanSino Biotechnology Inc, No other potential conflict of interest relevant to this article was reported.Ethics Approval Statement: The protocol and informed consent were approved by the Institutional Review Board of the Jiangsu Provincial Center of Disease Control and Prevention. Written informed consents from all participants were obtained before screening. This study was undertaken by Jiangsu Provincial Center of Disease Control and Prevention, Hubei Provincial Center for Disease Control and Prevention and Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology in accordance with the Declaration of Helsinki and Good Clinical Practice.