PROS1 and influenza: The approach by Kanekiyo et al. [45] has also been used to functionalize ferritin with HA derived from different influenza strains in search for a “universal” influenza vaccine [46,51,52], the trimeric envelope glycoprotein from HIV-1 (gp140) [9,63,78,79,80], and more recently, the spike (S) protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [81,82,83].