Skipping the Boundary Layer: High-Speed Droplet-Based Immunoassay Using Rayleigh Acoustic Streaming.

Acoustic mixing of droplets is a promising way to implement biosensors that combine high speed and minimal reagent consumption. To date, this type of droplet mixing is driven by a volume force resulting from the absorption of high-frequency acoustic waves in the bulk of the fluid. Here, we show that the speed of these sensors is limited by the slow advection of analyte to the sensor surface due to the formation of a hydrodynamic boundary layer. We eliminate this hydrodynamic boundary layer by using much lower ultrasonic frequencies to excite the droplet, which drives a Rayleigh streaming that behaves essentially like a slip velocity. At equal average flow velocity in the droplet, both experiment and three-dimensional simulations show that this provides a three-fold speedup compared to Eckart streaming. Experimentally, we further shorten a SARS-CoV-2 antibody immunoassay from 20 min to 40 s taking advantage of Rayleigh acoustic streaming.

SARS-CoV-2 infection-induced immunity reduces rates of reinfection and hospitalization caused by the Delta or Omicron variants.

During a pandemic, effective vaccines are typically in short supply, particularly at onset intervals when the wave is accelerating. We conducted an observational, retrospective analysis of aggregated data from all patients who tested positive for SARS-CoV-2 during the waves caused by the Delta and Omicron variants, stratified based on their known previous infection and vaccination status, throughout the University of Texas Medical Branch (UTMB) network. Next, the immunity statuses within each medical parameter were compared to naïve individuals for the effective decrease of occurrence. Lastly, we conducted studies using mice and pre-pandemic human samples for IgG responses to viral nucleocapsid compared to spike protein toward showing a functional component supportive of the medical data results in relation to the immunity types. During the Delta and Omicron waves, both infection-induced and hybrid immunities were associated with a trend of equal or greater decrease of occurrence than vaccine-induced immunity in hospitalizations, intensive care unit admissions, and deaths in comparison to those without pre-existing immunity, with hybrid immunity often trending with the greatest decrease. Compared to individuals without pre-existing immunity, those vaccinated against SARS-CoV-2 had a significantly reduced incidence of COVID-19, as well as all subsequent medical parameters. Though vaccination best reduces health risks associated with initial infection toward acquiring immunity, our findings suggest infection-induced immunity is as or more effective than vaccination in reducing the severity of reinfection from the Delta or Omicron variants, which should inform public health response at pandemic onset, particularly when triaging towards the allotment of in-demand vaccinations.

Recombinant chimpanzee adenovirus vector vaccine expressing the spike protein provides effective and lasting protection against SARS-CoV-2 infection in mice.

SARS-CoV-2 infection is a global public health threat. Vaccines are considered amongst the most important tools to control the SARS-CoV-2 pandemic. As expected, deaths from SARS-CoV-2 infection have dropped dramatically with widespread vaccination. However, there are concerns over the duration of vaccine-induced protection, as well as their effectiveness against emerging variants of concern. Here, we constructed a recombinant chimpanzee adenovirus vectored vaccine expressing the full-length spike of SARS-CoV-2 (AdC68-S). Rapid and high levels of humoral and cellular immune responses were observed after immunization of C57BL/6J mice with one or two doses of AdC68-S. Notably, neutralizing antibodies were observed up to at least six months after vaccination, without substantial decline. Single or double doses AdC68-S immunization resulted in lower viral loads in lungs of mice against SARS-CoV-2 challenge both in the short term (21 days) and long-term (6 months). Histopathological examination of AdC68-S immunized mice lungs showed mild histological abnormalities after SARS-CoV-2 infection. Taken together, this study demonstrates the efficacy and durability of the AdC68-S vaccine and constitutes a promising candidate for clinical evaluation.

Application of animal models to compare and contrast the virulence of current and future potential SARS-CoV-2 variants.

Since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified during late 2019, the sustained spread of this pathogen within the human population has caused worldwide disruption with staggering infection rates and death tolls. Due to the accumulation of mutations in SARS-CoV-2, the virus has evolved into many variants, five of which have been listed as variants of concern VOCs by the World Health Organization (WHO). Multiple animal models of SARS-CoV-2 have been developed to evaluate vaccines and drugs and to assess the pathogenicity, transmissibility and antiviral measures of these VOCs. Here, we review the cutting-edge research based on mouse, hamster, ferret and non-human primate models for evaluating SARS-CoV-2 with a focus on the Omicron variant, and highlight the importance of updating vaccines in a timely manner in order to mitigate the negative effects of SARS-CoV-2 infections in the human population.

Design of Replication-Competent VSV- and Ervebo-Vectored Vaccines Against SARS-CoV-2.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global public health emergency. Several vaccine candidates have been developed in response to the COVID-19 pandemic. One approach is to construct live-recombinant viruses expressing the SARS-CoV-2 spike protein (S) as vaccine candidates. The vesicular stomatitis virus (VSV) vector is a mature vaccine platform which was successfully developed as a vaccine against Ebola virus (EBOV), leading to its licensure by the Food and Drug Administration (FDA) in December 2019. Based on this work, we developed two live, replication-competent VSV-vectored vaccines against SARS-CoV-2: (1) a VSV expressing the S protein of SARS-CoV-2 and (2) a bivalent VSV expressing the S protein of SARS-CoV-2 and the glycoprotein (GP) of EBOV. This protocol describes the methodologies for the design, cloning, rescue, and preparation of these recombinant VSV vaccines.

Delayed specific IgM antibody responses observed among COVID-19 patients with severe progression.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly worldwide since it was confirmed as the causative agent of COVID-19. Molecular diagnosis of the disease is typically performed via nucleic acid-based detection of the virus from swabs, sputum or bronchoalveolar lavage fluid (BALF). However, the positive rate from the commonly used specimens (swabs or sputum) was less than 75%. Immunological assays for SARS-CoV-2 are needed to accurately diagnose COVID-19. Sera were collected from patients or healthy people in a local hospital in Xiangyang, Hubei Province, China. The SARS-CoV-2 specific IgM antibodies were then detected using a SARS-CoV-2 IgM colloidal gold immunochromatographic assay (GICA). Results were analysed in combination with sera collection date and clinical information. The GICA was found to be positive with the detected 82.2% (37/45) of RT-qPCR confirmed COVID-19 cases, as well as 32.0% (8/25) of clinically confirmed, RT-qPCR negative patients (4-14 days after symptom onset). Investigation of IgM-negative, RT-qPCR-positive COVID-19 patients showed that half of them developed severe disease. The GICA was found to be a useful test to complement existing PCR-based assays for confirmation of COVID-19, and a delayed specific IgM antibody response was observed among COVID-19 patients with severe progression.