Glycan shield densities were calculated using Proteins, Interfaces, Structures and Assemblies (PISA)83 analyses of fully glycosylated models of SARS S, MERS S, HKU1 S, LASV GPC, HIV-1 Env (BG505), Influenza H3N2 hemagglutinin (Victoria 2011), SIV Env (PDB ID 5X58, 5X59, 5I08, 5VK2, 4ZMJ, 4O5N, 6OHY, respectively)9,11,53,84–86. Oligomannose abundances of viral glycoproteins were ascertained by HILIC-UPLC analysis of PNGase F released N-linked glycans that were fluorescently labelled with procainamide24,45,53 (SI Fig. 5). The number of amino-acid residues interacting with N-linked glycans was divided by the number of solvent-accessible amino-acid residues of the glycoprotein as a measure for global glycan shield density. All viral glycoproteins analysed were expressed as trimers in HEK293F cells apart from LASV GPC, which was derived from virus-like particles from Madin-Darby canine kidney II cells.