@tom73 - Do you know how long the current covid booster takes to be effective? Yesterday it turns out I was in "close contact" ie not quite one metre, with someone who regularly travels to Denmark.
It's very subjective like most vaccines generally some effectiveness from a few days after and full immune memory kicks in around week or two. If I remember rightly you did feel unwell after you'd had it. Which tends to be a sign of a good immune response.
Close contact in it's self is not a certainty the risk of transmission very much depends on a number of factors.