Wrth wneud yr argymhelliad hwn, ystyriodd y Cyd-bwyllgor y data sydd ar gael o'r DU a gweddill y byd sy'n awgrymu bod imiwnedd pobl hŷn yn fwy tebygol o fynd yn wannach o ganlyniad i'r ffaith nad yw eu system imiwnedd yn gallu ymateb yn effeithiol i heintiau nac i frechlynnau i'r un graddau, a'u bod yn fwy tebygol o lawer o gael salwch difrifol os cânt eu heintio. Yn ymarferol, am eu bod wedi cael eu blaenoriaethu ar gyfer brechiadau ar ddechrau rhaglen brechu rhag COVID-19 yr hydref a ddechreuodd ym mis Medi 2022, mae rhagor o amser wedi mynd heibio ers i bobl hŷn gael eu dos diweddaraf o'r brechlyn.
In making this recommendation they considered available data from the UK and internationally which suggests that older people are more likely to experience waning of immunity due to a decreased capacity of the immune system to respond effectively to infections or vaccines, and much more likely to experience severe disease if infected. Practically, because they were prioritised for vaccination at the start of the COVID-19 Autumn booster programme that started in September 2022, older people are also now furthest in time from their last vaccine dose.