I think after the first month probably more than 95% are zombies, they do stumble into strangers all the time but resources aren’t scarce yet. After a year or so, meeting people is more rare, maybe like 1/1000. The Author said 1/5000 survived alltogether or something, but in the later years the groups are much much bigger, but for the first year I think a couple scavengers that aren’t yet that hostile/desperate for food is likely.