Bron studie Oxford University 02.12.2020 : https://academic.oup.com/.../ageing/afaa274/6016483...
"Little is known about the efficacy and safety of mRNA vaccines in older people, especially at the extremes of old age and in those with frailty.
A phase I study of the Moderna vaccine in ‘older adults’ published in the New England Journal of Medicine received considerable media attention after it found antibody responses were similar to those seen in younger people . However, this study included only 40 healthy people aged 58 or over, so its relevance to older people with frailty is unclear. Self-limiting mild to moderate adverse events were common, with all 20 participants aged 71 or over (mean age 72.6y) reporting local side effects such as pain at the injection site and 80% reporting systemic symptoms such as lethargy. Over 25% (around 8,000) participants of the Moderna phase III study are aged 65 or over and a similar proportion have chronic diseases, so the evidence base will improve once full interim results are published. For the Pfizer vaccine, published data on older participants are even more sparse. However, a press release from Pfizer claimed over 95% efficacy in their over-65 age group (but with no supporting details or figures)  and over 40% of participants in their Phase III trial are aged between 56 and 84.
B cell numbers remain more consistent with age but, due to a reduced expression of select proteins in old age, fewer functional antibodies are produced . Theoretically therefore, vaccines are likely to be somewhat less effective in older people. Moreover, the relative importance of cellular aspects of the immune response in COVD-19 is unclear, even more so in older people, so antibody levels may not be adequate surrogates for immunity . The impact of immunosenescence on vaccine safety is even more uncertain. Though the risk of serious adverse events mediated by over-activation of the immune system is theoretically lower, this may be offset by increased predisposition to adverse events overall, as this is the hallmark of frailty.