Thus, it is common to measure the OD across a series of typically 8-12 dilutions and report the dilution, known as the ‘endpoint’, at which the OD drops below a predefined baseline value. This enables high sample throughput but can limit resolution if the dilution used results in measurements near to the minimum or maximum Optical Density (OD) readout of the assay. Serology studies can be conducted using a single serum dilution in ELISA assays. The diverse nature of cohorts and variable circulation of HCoVs when cohorts were sampled may contribute to the sometimes conflicting reports. This observation tends to be weaker, absent, or even reversed when comparing cohorts of unmatched samples collected before and during the pandemic. Moreover, studies that measure sera collected longitudinally from COVID-19 patients show that SARS-CoV-2 infection increases serum antibody titers to certain beta-HCoV antigens, particularly OC43. Most studies that measure human sera collected before the COVID-19 pandemic demonstrate that a small proportion of pre-pandemic sera possess cross-reactive antibodies against the SARS-CoV-2 S1S2 and N antigens. Several studies have now measured reactivity of human serum collected before and during the COVID-19 pandemic, and through the course of SARS-CoV-2 infections against panels of HCoV antigens. Furthermore, if cross-reactivity did exist, it was not known how protective it may be against SARS-CoV-2 infection. It was also unknown how much cross-reactivity there was between antibodies elicited to prior HCoV infections against SARS-CoV-2. The SARS-CoV outbreak in 2003 was largely contained and MERS-CoV is not well adapted for ongoing human to human transmission.Īt the start of the COVID-19 pandemic we lacked detailed knowledge of serological reactivity to HCoVs in the human population. Two other beta-CoVs have also infected humans: severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV). These are the alpha-CoVs HCoV-229E (229E) and HCoV-NL63 (NL63), and the beta-CoVs HCoV-HKU1 (HKU1) and HCoV-OC43 (OC43). Four CoVs circulate continuously in humans (HCoVs), are distributed globally, and generally cause common cold or influenza-like illness. Ĭoronaviruses (CoVs) more generally are separated into four phylogenetic clades: alpha-CoV, beta-CoV, gamma-CoV and delta-CoV.
The World Bank estimates that between 119 and 124 million people were pushed into extreme poverty by impacts of the COVID-19 pandemic in 2020 alone. On March 11, 2020, the outbreak was declared a pandemic by the World Health Organization (WHO) and at the time of writing there have been over 206 million confirmed SARS-CoV-2 infections and 4.3 million deaths attributed to the virus globally. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 and is the causative agent of coronavirus disease 2019 (COVID-19).
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