From recent observatory studies, SIREN in UK , and in Denmark, they both estimate seropositivity to give around 80% of protection agains infection. The former observed 90% protection against symptomatic cases.
How efficacious are vaccines on the seropositive population? I’ve only seen reports on safety analysis.
To the extend of suspecting malice, the Israel Pfizer study did not report on prior infection analysis—Study protocol states “Exclusion of patients with COVID-19 prior to the index date or matched index date.”