What is the immunity against covid 19, after first shot of phizer and how long to you build that? i know evidence changes all the time though. thank you?

After the first "jab", there appears to be about 50% efficacy, but the second injection solidifies efficacy at roughly 95%. So, in spite of varying comments on 2 injections in the media and online, do not deviate from the original plan and get your second injection on schedule.

“Pfizer's shot was 52.4% effective at protecting against COVID-19 wi symptoms between the 1st & 2nd dose, according to the FDA documents. But the 52.4% figure includes the 11 days before protection kicks in after the first dose, so the real percentage could well be higher.” REF: https://www.businessinsider.com/covid-vaccine-one-shot-effectiveness-pfizer-moderna-astrazeneca-vaccines-dose-2021-3