Against 'normal' COVID they are much more effective (I've read 89%/86% for Pfizer/AZ after one jab). Against the Indian varieties they struggle, particularly delta.
From what I've read, they are still doing the research on that. There is some evidence that there is a lower amount of measurable antibodies, but that doesn't necessarily mean lower efficacy.
Kappa died out in India, interesting that Delta is the problem in the UK now.
Reading the stuff from the UK, the conclusion is that Delta has a higher R0, and that means it is even more important to have both doses of the vaccine as they know that cuts transmission. They are concerned that higher rates of transmission could lead to the NHS being overwhelmed again.
Pfizer jab recipients have lower antibodies targeting Indian variant
People who have had the Pfizer vaccine have lower antibody levels targeting the Indian variant, also known as Delta, than those against previously circulating variants in the UK, new data suggests.
www.standard.co.uk
The conclusion - as always - is get vaccinated. Roll out the vaccination program more quickly.