select search filters
roundups & rapid reactions
before the headlines
Fiona fox's blog

expert reaction to study looking at how and when protection wanes after two doses of the Oxford-AstraZeneca COVID-19 vaccine

A study published in the Lancet looks at protection of two doses of the Oxford-AstraZeneca vaccine against COVID-19 hospital admissions and deaths over time.


Prof Penny Ward, Independent Pharmaceutical Physician, and Visiting Professor in Pharmaceutical Medicine at King’s College London, said:

“This paper is focused on the vaccine effectiveness over time following completion of a course of the ChAdOx01 vaccine and estimates change in protection against more severe outcomes relative to protection offered within the first 2-3 weeks of completion of the course.  It is not surprising, given previously observed reduction in protection against symptomatic, non severe disease as time from completion of the primary course progresses, that protection against more severe disease also diminishes as the period since completion of the course gets longer.  The paper focuses on relative rates of these serious outcomes which give a rather alarming impression at first glance – it takes some effort to understand that there is in fact sustained vaccine effectiveness in preventing hospitalisation and death from COVID of at least 50% across the period of follow up.  In addition, it appears that the absolute incidence of these outcomes is also, thankfully, low.  Nonetheless the data reiterate, as we already know, that a booster vaccination shot is required to confer higher levels of sustained protection and indeed everyone should ensure they get out and get boosted as fast as possible to retain protection against covid illness of any severity, particularly given the spread of the omicron variant and the desire to mix with family and friends over the festive period.”



‘Two-dose ChAdOx1 nCoV-19 vaccine protection against COVID-19 hospital admissions and deaths over time: a retrospective, population-based cohort study in Scotland and Brazil’ by Srinivasa Vittal Katikireddi et al. was published in the Lancet at 23:30 UK time on Monday 20 December 2021.

DOI: 10.1016/S0140-6736(21)02754-9



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Penny Ward: “I am semi-retired, but I am owner/Director of PWG Consulting (Biopharma) Ltd a consulting firm advising companies on drug and device development. Between December 2016 and July 2019 I served as Chief Medical Officer of Virion Biotherapeutics Ltd, a company developing antiviral treatments for respiratory viral diseases. Previous employee of Roche, makers of tocilizumab (anti IL6 antibody) and CMO of Novimmune, makers of empalumab (anti IFN gamma antibody).”



in this section

filter RoundUps by year

search by tag