Unfortunately, the boosters were not 'tuned' for Delta. They are basically the same as the first doses. However, I read some of the data and it appears that a 'boost', especially for those with weaker immune responses to the original vaccines, can bring the efficacy back up into the 80s% range for Delta.
Think about this for a moment, there is some good news about the Delta variant. Because it's so contagious, it's taken over 95+% of the new cases. It would take an even more contagious version to overtake it OR a variant that is majorly resistant to the current vax - BOTH of these scenarios can be prevented by getting every available vaccine to large 3rd world populations to prevent the India-level event that spawned Delta (I don't particularly like the WHO, but they are absolutely right about this one). Every wealthy country should be flying BUS LOADS of vaccines to these areas EVERY DAY.
If all stays status quo in the world, Delta will burn out and COVID 19 will finally be behind us by end of mid-Spring (my guess).
Can I get an AMEN?