Assessing Immune Response of Different COVID-19 Vaccines in Older Adults

This is a randomised controlled, adaptive, multicentre Phase II protocol evaluating different booster strategies in individuals aged 75 years and older already vaccinated against SARS-CoV-2. Part A of this trial foresees testing of different vaccines as a 3rd vaccination dose (first booster) for comparative assessment of their immunogenicity and safety against SARS-CoV-2 wild-type and variants in the elderly, a usually neglected population. Part B of this trial foresees testing of different vaccines as a 4th vaccination dose (second booster) for comparative assessment of their immunogenicity and safety against SARSCoV-2 wild-type and variants in the identical population.

Part A of the present trial in which individuals received a 3rd vaccination (first booster) of either BNT162b2 or mRNA-1273 was closed to further recruitment as of January 13, 2022. This was due to a change in vaccination policies, recommending a 3rd vaccination with either BNT162b2 or mRNA-1273. Therefore, Part A was supplanted by Part B that investigated a 4th COVID-19 vaccination and started on 21 Jan 2022. The initial study protocol started the trial with Part A in which participants were randomized to a 3rd vaccination (first booster) with either BNT162b2 or mRNA-1273: Subjects who - prior to study entry - received a vaccination series of either BNT162b2 \& BNT162b2 or mRNA-1273 \& mRNA-1273 or ChAdOx-1-S \& ChAdOx-1-S. For the reasons mentioned above, the study protocol was amended to continue the trial with Part B in which participants were randomized to a 4th vaccination (second booster) with either BNT162b2 or mRNA-1273: Subjects who - prior to study entry - received a vaccination series of either BNT162b2 \& BNT162b2 \& BNT162b2 or BNT162b2 \& BNT162b2 \& mRNA-1273 or mRNA-1273 \& mRNA-1273 \& mRNA-1273 or mRNA-1273 \& mRNA-1273 \& BNT162b2 or ChAdOx-1-S \& ChAdOx-1-S \& BNT162b2 or ChAdOx-1-S \& ChAdOx-1-S \& mRNA-1273.