Persistence of the immune response after two doses of ChAdOx1 nCov-19 (AZD1222): 1 year of follow-up of two randomized controlled trials

Merryn Voysey, Amy Flaxman*, Jeremy Aboagye, Parvinder K. Aley, Sandra Belij-Rammerstorfer, Sagida Bibi, Mustapha Bittaye, Federica Cappuccini, Sue Charlton, Elizabeth A. Clutterbuck, Sophie Davies, Christina Dold, Nick J. Edwards, Katie J. Ewer, Saul N. Faust, Pedro M. Folegatti, Jamie Fowler, Ciaran Gilbride, Sarah C. Gilbert, Leila GodfreyBassam Hallis, Holly E. Humphries, Daniel Jenkin, Simon Kerridge, Yama F. Mujadidi, Emma Plested, Maheshi N. Ramasamy, Hannah Robinson, Helen Sanders, Matthew D. Snape, Rinn Song, Kelly M. Thomas, Marta Ulaszewska, Danielle Woods, Daniel Wright, Andrew J. Pollard, Teresa Lambe

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


The trajectory of immune responses following the primary dose series determines the decline in vaccine effectiveness over time. Here we report on maintenance of immune responses during the year following a two-dose schedule of ChAdOx1 nCoV-19/AZD1222, in the absence of infection, and also explore the decay of antibody after infection. Total spike-specific IgG antibody titres were lower with two low doses of ChAdOx1 nCoV-19 vaccines (two low doses) (P = 0.0006) than with 2 standard doses (the approved dose) or low dose followed by standard dose vaccines regimens. Longer intervals between first and second doses resulted in higher antibody titres (P < 0.0001); however, there was no evidence that the trajectory of antibody decay differed by interval or by vaccine dose, and the decay of IgG antibody titres followed a similar trajectory after a third dose of ChAdOx1 nCoV-19. Trends in post-infection samples were similar with an initial rapid decay in responses but good persistence of measurable responses thereafter. Extrapolation of antibody data, following two doses of ChAdOx1 nCov-19, demonstrates a slow rate of antibody decay with modelling, suggesting that antibody titres are well maintained for at least 2 years. These data suggest a persistent immune response after two doses of ChAdOx1 nCov-19 which will likely have a positive impact against serious disease and hospitalization.

Original languageEnglish
Pages (from-to)280-287
Number of pages8
JournalClinical and Experimental Immunology
Issue number3
Publication statusPublished - Mar 2023

Bibliographical note

Publisher Copyright:
© The Author(s) 2023. Published by Oxford University Press on behalf of the British Society for Immunology.


  • anti-viral immunity
  • antibodies
  • vaccination
  • vaccine


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