There are several diseases your puppy is vulnerable to before being fully vaccinated, and it can only be vaccinated at certain ages (see below). Diseases can be caught from other dogs’ poo and wee, so don’t risk it.
So, from when collecting the puppy at 8 weeks, to its final in the series of puppy vaccinations at 12 weeks, the puppy must not be taken to any public areas (public parks, footpaths, shopping areas – anywhere other dogs go). So, that period is ideal to focus on internal socialisation with people (or other dogs if you know they have been vaccinated).