ACKNOWLEDGEMENTS

This work was supported by Sheffield Teaching Hospitals NHS Foundation Trust, UK. The authors are grateful to Prof. Florian Krammer (Icahn School of Medicine at Mount Sinai, New York) for providing the spike plasmid via Dr. Thushan de Silva (University of Sheffield), Martin Nicklin (University of Sheffield) for providing the Expi293F cells, Molly Smith (University of Sheffield) for a preliminary test of HEK transfection procedures, Prof. William Egner (Sheffield Teaching Hospitals) for support and help with ELISA development work and validation. MJD acknowledges support from the Biotechnology and Biological Sciences Research Council UK (BBSRC) (BB/M012166/1).
Declarations of interest: The authors declare no conflict of interest.