> Be careful with your second study, because they looked at those that developed/still had antibodies post-infection. Kinda like saying those that developed a good immune response developed a good immune response.

True. It depends on which specific antibody you look for, and how.

Here's a recent cohort study:

Anti-SARS-CoV-2 Antibodies Persist for up to 13 Months and Reduce Risk of Reinfection https://www.medrxiv.org/content/10.1101/2021.05.07.21256823v...

"Here, we longitudinally measured Spike (S) and Nucleocapsid (N)-specific antibodies in 1,309 healthcare workers (HCWs), including 916 COVID-19 negative HCWs and 393 convalescent COVID-19 for up to 422 days post-symptom. ... Overall, 69 SARS-CoV-2 infections developed in the COVID-19 negative group (incidence of 12.22 per 100 person-years) versus one in the COVID-19 positive group (incidence of 0.40 per 100 person-years), indicating a relative reduction in the incidence of SARS-CoV-2 reinfection of 96.7% (p<0.0001)."

Of course, these antibodies <--> protection studies are a bit of streetlamp effect phenomenon. Antibodies are relatively easy to measure so that's what immune endurance studies tend to check for. The relative risk of reinfection in real-world settings is the more robust measure.