A multiplexed Cas13-based assay with point-of-care attributes for simultaneous COVID-19 diagnosis and variant surveillance (preprint)

Point-of-care (POC) nucleic acid detection technologies are poised to aid gold-standard technologies in controlling the COVID-19 pandemic, yet shortcomings in the capability to perform critically needed complex detection, such as multiplexed detection for viral variant surveillance, may limit their widespread adoption. Herein, we developed a robust multiplexed CRISPR-based detection using LwaCas13a and PsmCas13b to simultaneously diagnose SARS-CoV-2 infection and pinpoint the causative SARS-CoV-2 variant of concern (VOC)-including globally dominant VOCs Delta (B.1.617.2) and Omicron (B.1.1.529)-all while maintaining high levels of accuracy upon the detection of multiple SARS-CoV-2 gene targets. The platform has several attributes suitable for POC use: premixed, freeze-dried reagents for easy use and storage; convenient direct-to-eye or smartphone-based readouts; and a one-pot variant of the multiplexed detection. To reduce reliance on proprietary reagents and enable sustainable use of such a technology in low- and middle-income countries, we locally produced and formulated our own recombinase polymerase amplification reaction and demonstrated its equivalent efficiency to commercial counterparts. Our tool, CRISPR-based detection for simultaneous COVID-19 diagnosis and variant surveillance which can be locally manufactured, may enable sustainable use of CRISPR diagnostics technologies for COVID-19 and other diseases in POC settings.

SARS-CoV-2 variants of concern exhibit reduced sensitivity to live-virus neutralization in sera from CoronaVac vaccinees and naturally infected COVID-19 patients (preprint)

Recent surges in SARS-CoV-2 variants of concern (VOCs) call for the need to evaluate levels of vaccine- and infection- induced SARS-CoV-2 neutralizing antibodies (NAbs). CoronaVac (Sinovac Biotech, Beijing, China) is currently being used for mass vaccination in Thailand as well as other low-income countries. Three VOCs currently circulating within Thailand include the B.1.1.7 (Alpha), B.1.351 (Beta), and B.1.617.2 (Delta) strains. We assessed NAb potency against the prototypic strain containing the original spike sequence (WT) compared to that against the 3 VOCs using sera derived from a cohort of healthcare workers who received a full 2-dose regimen of CoronaVac. Sera from two other cohorts consisting of COVID-19 patients who had been hospitalized in 2020 and 2021 were evaluated for comparison. We found that, despite equally robust production of S1-RBD-binding IgG and 100% seropositivity, sera from both CoronaVac vaccinees and naturally infected individuals had significantly reduced neutralizing capacity against all 3 VOCs compared to WT. Strikingly, NAb titers against Alpha and Beta were comparable, but Delta appears to be significantly more refractory to NAbs in all groups. Our results may help inform on CoronaVac NAb-inducing capacity, which is a proxy for vaccine efficacy, in the context of the WT strain and 3 VOCs. Our results also have critical implications for public health decisionmakers who may need to maintain efficient mitigation strategies amid a potentially high risk for infection with VOCs even in those who have been previously infected.