How is SARS-CoV-2 'deactivated' for some Covid vaccines (for example Covaxin)? Some Covid vaccines like Covaxin employ a 'Whole-Virion Inactivated Vero Cell'. How is the virion 'deactivated' for the vaccine?

For Covaxin (BBV152), SARS-CoV-2 was inactivated by treatment with β-propiolactone [1]. β-propiolactone reacts with and modifies, among other things, nucleic acids, thus preventing their replication [2].

[1] Yadav P, Ella R, Kumar S, et al. 2020. Remarkable immunogenicity and protective efficacy of BBV152, an inactivated SARS-CoV-2 vaccine in rhesus macaques. Preprint.

[2] Perrin P, Morgeaux S. 1995. Inactivation of DNA by β-propiolactone. Biologicals 23(3):207-211.