The SARS-CoV-2 virus infects cells very effectively, especially epithelial cells lining the respiratory tract and salivary gland. It is not surprising that vaccinated people are tested positive and there is nothing to worry about. Vaccines still offer protection by reducing the viral load and preventing serious cases. Another thing that bothers me is why people are so obsessed with antibody level. Humoral response only constitutes part of our immunity and we also have memory cells when we are reinfected.I wonder how long post their second shot they tested positive? Of course no vaccine is 100% effective. Even those that are close e.g. rabies don't always result in a high level of immunity, especially if there are immune system issues involved. I once had to leave my dog in overseas and domestic quarantine for 6 months as I had to have her vaccinated again and then wait for over 3 months before bringing her back as her rabies vaccine hadn't produced a very high level of antibodies (shot only required for entry but a specific antibody limit required for return into Australia.). She suffered occasionally from lupus and had to take immune suppressants when she has an outbreak.
The massive decline in deaths in the UK has to be hugely related to the mass vaccination even if summer helped. As long as the pace of vaccination keeps up the death toll shouldn't retunr to anywhere near what it was and we also have new variant vaccines not that far away for next year.
https://doi.org/10.1016/j.chom.2021.02.019