Sorry to hear this Hurdity. I hope that he recovers quickly. You do need two doses for better protection but I can't remember the percentage difference between the first and second doses. Must be online somewhere!
Having both doses is supposed to keep even elderly people (over 60) out of hospital but, yes, being fully vaccinated doesn't mean you won't catch it or transmit it which is where the current social distancing rules are supposed to protect us.
I feel it would be useful for us if data was published as to how many current cases have had either none, one or two doses.
Taz x