Because it is the weakest example of a vaccine in history. Numbers out of the UK are the Covax has 65% to 35% efficacy against Delta at 2 months post vax and 35% to 5% efficacy at 6 months. Its easy to see why so many double jagged are getting seriously ill. Perhaps they should consider boosters every 3 months.
I ask again...are we really still calling this a vaccine? It maybe should be called a therapy with potential short term injuries and unknown mid term to long term injuries.