This is covered in the FAQ but I will post here as well.
Q: I know that CCSA certification is a prerequisite for CCSE. Can I achieve a CCSE R80 certification with a CCSA R70 or R77 certification?
A: No. Since R80 is a completely new product version with many new features, only the CCSA R80 certification provides the background necessary to be a prerequisite to CCSE R80 certification.
However, any CCSE R77 or older is eligible to take our upgrade exam #156-915.80 to earn your CCSE R80 certification.
So it's your choice-either get CCSE R77 then the upgrade exam, or do the R80 CCSA and then R80 CCSE.