Indian Covid vaccine Covaxin

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A NYT article about the vaccine says as folllows:

To create Covaxin, Bharat Biotech used a sample of the coronavirus isolated by India’s National Institute of Virology. Once the researchers produced large stocks of the coronaviruses, they doused them with a chemical called beta-propiolactone. The compound disabled the coronaviruses by bonding to their genes. The inactivated coronaviruses could no longer replicate. But their proteins, including spike, remained intact.

https://www.nytimes.com/interactive/2021/health/bharat-biotech-covid-19-vaccine.html

How reliable is the chemical reaction? Does it bind to every single one of the virions or there could be a small amount - say 1% or 0.001% - which remains intact?