The Phase III efficacy trials did not enroll any adults age 90 or over from what I understand. I don't believe any person age 90 or older would be refused the vaccine, but the effectiveness of it may be less. As we age (me included) our immune systems slowly, progressively begin to slow down and auto immune disorders gradually increase in the elderly. Therefore, the Covid-19 vaccine from Pfizer (and essentially the same vaccine from Moderna) may be less efficient for older individuals. However, with that said and given the average age of mortality from Covid-19 is 83, I would surely opt for the vaccine for my parents if they were both still alive and over the age of 90.