Vaccinating people who have had covid-19: why doesn’t natural immunity count in the US? published September 2021 by Block shows 20 studies support natural immunity is robust, complete and durability and far superior to vaccine induced immunity.
Risks of Vaccines for Those Recovered from COVID-19 – Krammer, Raw & Mathioudakis published September 2021 by McCullough, summarizes 3 studies (6 total) showing if we vaccinate people who have recovered from COVID-19, we harm them considerably.