Is the 95% efficacy from pfizer (or % from covid vaccines in general) able to fluctuate much? is 95% an average but a poor immune system could have a much lower immune response? or is @ least around 95% basically guaranteed by full vaccination?

Taking vaccine is better than not taking it. Vaccination prevented serious illness and death in virtually all recipients. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV and Covid vaccines. Wish you good health!