Dr John Cambell has been saying this for months - initially based on results from people who had recovered from SARS (still have memory T-cells after 17 years), and more recently based on a study of HCP’s who contracted Covid in the first wave, none of whom got it in the second (although plenty of their previously uninfected colleagues did).
I’m fighting off the rona at the moment - but I’ll still roll my sleeve up when they offer me the vaccine.