“2) it is clear that unvaccinated are threat to vaccinated“
coffee: What is the “threat”? That they get a cold?
A fair question. Depends on the recipient. The good news for un-vaxed would be that if indeed vaxed people do not transmit much under reasonable conditions, then un-vaxed need to worry “only” about one contact. So, if you are in contact with only healthy young people, then indeed most of them would only get a cold and probably will not transmit to their friends who will transmit to the grandmas … If you are working or davening or in any other pro-longed contact with old or possibly unhealthy people, then they can still get seriously sick.