Comparison of SARS-CoV-2 variants in primary human nasal cultures indicates Delta as most cytopathic and Omicron as fastest replicating (preprint)

The ongoing SARS-CoV-2 pandemic has been marked with emerging viral variants, some of which were designated as variants of concern (VOCs) due to their selection and rapid circulation in the human population. Here we elucidate functional features of each VOC in patient-derived primary nasal cultures grown at air-liquid-interface (ALI) to model upper-respiratory infection, and human lung epithelial cell lines to model lung infection. All VOCs replicated to higher titers than the ancestral virus, and Omicron reached the higher titer in the upper-respiratory system in both nasal cells and parallel human studies. Delta was most adept at cell-to-cell spread and the most cytopathic to nasal cells by compromising cell-barrier integrity and ciliary beating. All VOCs overcame dsRNA-activated cellular responses including interferon signaling, oligoadenylate ribonuclease L (OAS-RNase L) degradation and protein kinase R (PKR) activation. Our findings highlight the functional differences among VOCs and illuminate distinct mechanisms of pathogenesis in infected individuals.

Variations in COVID-19 impacts by social vulnerability in Philadelphia, June 2020-December 2022 (preprint)

Introduction: The study objective was to elucidate the relationship between social vulnerability and COVID-19 impacts in Philadelphia between June 2020 and December 2022. Methods: Using publicly available COVID-19 case, test, hospitalization, and mortality data for Philadelphia (June 7, 2020-December 31, 2022) and area-level social vulnerability data, we compared the incidence, test positivity, hospitalization, and mortality rates in high and low vulnerability neighborhoods of Philadelphia, characterized as scoring above or below the national median score on the social vulnerability index. We used linear mixed effects models to test the association between social vulnerability and COVID-19 incidence, test positivity, hospitalization, and mortality rates, adjusting for time and age distribution. Results: 90.4% of Philadelphians (n = 1,430,153) live in neighborhoods classified as socially vulnerable, based on scoring above the national median score on the social vulnerability index. COVID-19 incidence, hospitalization, and mortality rates were significantly elevated in the more vulnerable communities, with p < 0.05, p < 0.005, and p < 0.001, respectively. The relative risks of COVID-19-related incidence, hospitalization, and death, comparing the more vulnerable neighborhoods to the less vulnerable neighborhoods, were 1.11 (95%CI: 1.10-1.12), 2.07 (95%CI: 1.93-2.20), and 2.06 (95%CI: 1.78-2.38), respectively. Thus, between June 7, 2020 and December 31, 2022, 32,573 COVID-19 cases, 9,409 hospitalizations, and 1,967 deaths would have been avoided in Philadelphias more vulnerable communities had they experienced the same rates of incidence, hospitalization, and death as the less vulnerable Philadelphia communities. Conclusions: These results highlight the disparate morbidity and mortality experienced by people living in more vulnerable neighborhoods in a large US city. Importantly, our findings illustrate the importance of designing public health policies and interventions with an equity-driven approach, with greater resources and more intensive prevention strategies applied in socially vulnerable communities.

Evolutionary Trajectories of SARS-CoV-2 Alpha and Delta Variants in White-Tailed Deer in Pennsylvania (preprint)

The SARS-CoV-2 pandemic likely began by spillover from bats to humans; today multiple animal species are known to be susceptible to infection. White-tailed deer, Odocoileus virginianus are infected in the United States at substantial levels, raising concerns about the formation of a new animal reservoir and potential of spill-back of new variants into humans1. Here we characterize SARS CoV-2 in deer from Pennsylvania (PA) sampled during fall and winter 2021. Of 93 nasal swab samples analyzed by RT-qPCR, 18 (19.3%) were positive for SARS-CoV-2. Seven whole-genome sequences were obtained, which were annotated as alpha and delta variants, the first reported observations of these lineages in deer, documenting multiple new jumps from humans to deer. The alpha lineage persisted in deer after its displacement by delta in humans, and deer-derived alpha variants diverged significantly from those in humans, consistent with a distinctive evolutionary trajectory in deer.

SARS-CoV-2 variants associated with vaccine breakthrough in the Delaware Valley through summer 2021 (preprint)

The severe acute respiratory coronavirus-2 (SARS-CoV-2) is the cause of the global outbreak of COVID-19. Evidence suggests that the virus is evolving to allow efficient spread through the human population, including vaccinated individuals. Here we report a study of viral variants from surveillance of the Delaware Valley, including the city of Philadelphia, and variants infecting vaccinated subjects. We sequenced and analyzed complete viral genomes from 2621 surveillance samples from March 2020 to September 2021 and compared them to genome sequences from 159 vaccine breakthroughs. In the early spring of 2020, all detected variants were of the B.1 and closely related lineages. A mixture of lineages followed, notably including B.1.243 followed by B.1.1.7 (alpha), with other lineages present at lower levels. Later isolations were dominated by B.1.617.2 (delta) and other delta lineages; delta was the exclusive variant present by the last time sampled. To investigate whether any variants appeared preferentially in vaccine breakthroughs, we devised a model based on Bayesian autoregressive moving average logistic multinomial regression to allow rigorous comparison. This revealed that B.1.617.2 (delta) showed three-fold enrichment in vaccine breakthrough cases (odds ratio of 3; 95% credible interval 0.89-11). Viral point substitutions could also be associated with vaccine breakthroughs, notably the N501Y substitution found in the alpha, beta and gamma variants (odds ratio 2.04; 95% credible interval of 1.25-3.18). This study thus provides a detailed picture of viral evolution in the Delaware Valley and a geographically matched analysis of vaccine breakthroughs; it also introduces a rigorous statistical approach to interrogating enrichment of viral variants.

Molecular beacons allow specific RT-LAMP detection of B.1.1.7 variant SARS-CoV-2 (preprint)

Over the course of the COVID-19 pandemic, several SARS-CoV-2 genetic variants of concern have appeared and spread throughout the world. Detection and identification of these variants is important to understanding and controlling their rapid spread. Current detection methods for a particularly concerning variant, B.1.1.7, require expensive qPCR machines and depend on the absence of a signal rather than a positive indicator of variant presence. Here we report an assay using a pair of molecular beacons paired with reverse transcription loop mediated amplification to allow isothermal amplification from saliva to specifically detect B.1.1.7 and other variants which contain a characteristic deletion in the gene encoding the viral spike protein. This assay is specific, affordable and allows multiplexing with other SARS-CoV-2 LAMP primer sets.

LAMP-BEAC: Detection of SARS-CoV-2 RNA Using RT-LAMP and Molecular Beacons (preprint)

SARS-CoV-2 has caused a global pandemic, resulting in the need for rapid assays to allow diagnosis and prevention of transmission. Reverse Transcription-Polymerase Chain Reaction (RT-PCR) provides a gold standard assay for SARS-CoV-2 RNA, but tests are expensive and supply chains are potentially fragile, motivating interest in additional assay methods. Reverse transcription and Loop Mediated Isothermal Amplification (RT-LAMP) provides an alternative that uses alternative and often cheaper reagents without the need for thermocyclers. The presence of SARS-CoV-2 RNA is typically detected using dyes to report bulk amplification of DNA; however a common artifact is nonspecific DNA amplification, complicating detection. Here we describe the design and testing of molecular beacons, which allow sequence-specific detection of SARS-CoV-2 genomes with improved discrimination in simple reaction mixtures. We also show how beacons with different fluorescent labels can allow convenient multiplex detection of several amplicons in "single pot" reactions.