Table 1. The four serological assays used in this study.

Assay	Antigen	Serum dilution	Readout
ELISA N	N	1:200	Optical density
ELISA tri-S	Trimeric S	1:400	Optical density
S-Flow	S at the cell surface	1:300	Flow cytometry
LIPS	S1 and N	1:10	Bioluminescence (luciferase)