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.