...the only places you go are supermarkets (maybe three times a week), no public transport, and no prolonged contact with anyone outside your household?
This is how we're currently living - we're in a lockdown area but we don't have any family or friends anyway, so we haven't really had any contact beyond people we walk past in supermarkets for months. DH is wfh, I don't work and DD lost her job at the start of lockdown and hasn't found anything else so she's going out even less than me. We all SD when we're out, are fastidious about hygiene and DH and DD wear masks in public (I'm exempt).
As I understand it, you need to spend a good few minutes in fairly close contact with someone who's infected to catch it, and none of us have done that for ages. We're in a high risk area and I'm higher risk myself (autoimmune condition) - our rate locally is over 300 per 100,000 and I'm even more concerned now than I was in April. I've been quite calm about everything so far actually, but in the last few days my anxiety has rocketed. So, sorry for the inane questions! Just trying to reassure myself really.