A multinational, phase 2, randomised, adaptive protocol to evaluate immunogenicity and reactogenicity of different COVID-19 vaccines in adults ≥75 already vaccinated against SARS-CoV-2 (EU-COVAT-1-AGED): a trial conducted within the VACCELERATE network

Trials. 2022 Oct 8;23(1):865. doi: 10.1186/s13063-022-06791-y.


Background: In the ongoing COVID-19 pandemic, advanced age is a risk factor for a severe clinical course of SARS-CoV-2 infection. Thus, older people may benefit in particular from booster doses with potent vaccines and research should focus on optimal vaccination schedules. In addition to each individual's medical history, immunosenescence warrants further research in this population. This study investigates vaccine-induced immune response over 1 year.

Methods/design: EU-COVAT-1-AGED is a randomised controlled, adaptive, multicentre phase II protocol evaluating different booster strategies in individuals aged ≥75 years (n=600) already vaccinated against SARS-CoV-2. The initial protocol foresaw a 3rd vaccination (1st booster) as study intervention. The present modified Part B of this trial foresees testing of mRNA-1273 (Spikevax®) vs. BNT162b2 (Comirnaty®) as 4th vaccination dose (2nd booster) for comparative assessment of their immunogenicity and safety against SARS-CoV-2 wild-type and variants. The primary endpoint of the trial is to assess the rate of 2-fold antibody titre increase 14 days after vaccination measured by quantitative enzyme-linked immunosorbent assay (Anti-RBD-ELISA) against wild-type virus. Secondary endpoints include the changes in neutralising antibody titres (Virus Neutralisation Assay) against wild-type as well as against Variants of Concern (VOC) at 14 days and up to 12 months. T cell response measured by qPCR will be performed in subgroups at 14 days as exploratory endpoint. Biobanking samples are being collected for neutralising antibody titres against potential future VOC. Furthermore, potential correlates between humoral immune response, T cell response and neutralising capacity will be assessed. The primary endpoint analysis will be triggered as soon as for all patients the primary endpoint (14 days after the 4th vaccination dose) has been observed.

Discussion: The EU-COVAT-1-AGED trial Part B compares immunogenicity and safety of mRNA-1273 (Spikevax®) and BNT162b2 (Comirnaty®) as 4th SARS-CoV-2 vaccine dose in adults ≥75 years of age. The findings of this trial have the potential to optimise the COVID-19 vaccination strategy for this at-risk population.

Trial registration: ClinicalTrials.gov NCT05160766 . Registered on 16 December 2021.

Protocol version: V06_0: 27 July 2022.

Keywords: Advanced age; BNT162b2 (Comirnaty®); Booster; COVID-19 vaccination; Fourth dose; Immunosenescence; Phase II; Randomisation; SARS-CoV-2; VOC; Variants of concern; mRNA-1273 (Spikevax®); ≥75 years.

Publication types

  • Clinical Trial Protocol

MeSH terms

  • Adult
  • Aged
  • Antibodies, Neutralizing
  • Antibodies, Viral
  • BNT162 Vaccine
  • Biological Specimen Banks
  • COVID-19 Vaccines / adverse effects
  • COVID-19* / prevention & control
  • Clinical Trials, Phase II as Topic
  • Humans
  • Pandemics / prevention & control
  • Randomized Controlled Trials as Topic
  • SARS-CoV-2
  • Vaccines*


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • COVID-19 Vaccines
  • Vaccines
  • BNT162 Vaccine

Associated data

  • ClinicalTrials.gov/NCT05160766