Expert reaction to press release from the ZOE app on vaccine effectiveness over time


A press release from the ZOE COVID Study suggests that vaccine protection provided by two doses of the Pfizer-BioNTech and Oxford-AstraZeneca COVID-19 vaccines is waning in the first vaccinated.

Dr Peter English, Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice, Immediate past Chair of the BMA Public Health Medicine Committee, said:

“The press release is disappointing. As far as I can tell, it refers only to effectiveness against (any) infection. It doesn’t go into detail in the press release itself – you’d have to read and understand the papers it links to – but I assume “infection” means “confirmed infection”, ie people who report having tested positive.

“There are various ways in which vaccines can or might be effective. They might prevent infection altogether (and thereby onward transmission); they can reduce the duration, and level, of infectiousness in people who, despite vaccination, become infected; and they can prevent minor symptomatic infection (cough/cold/headache), more serious flu-like illness not requiring hospitalisation, illness severe enough to require hospitalisation, illness severe enough to require critical care (ICU admission), and death.

“There is a world of difference between efficacy against, on the one hand, any infection and on the other hand, illness severe enough to require hospitalisation, critical care, or to cause death.

“I am disappointed that the press release failed to tease out these differences, to explain more clearly what it means by “infection risk reduction”, and to comment on effectiveness against different outcomes.”

Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, said:

“The ZOE app is a useful tool in monitoring people’s symptoms and that is what it relies on for its data, but on its own it cannot accurately monitor the number of infections in the population, as some have claimed.

“The app is dependent on a self-selecting cohort, so even though the sample size is large, it does not necessarily use a study group which is reflective of the UK population.

“Therefore these data are likely to be under-reporting infections as anyone with the virus but without symptoms, won’t be reporting this to the app.  It seems likely that the ZOE app would therefore lead to over-reporting of the protection given by the vaccines.

“It is also hard to compare infection rates between May and July in the UK and claim the difference is due to waning effects of vaccination, when wider community infections were more than eight times higher on 31 July (when there were 26144 new daily cases) than on 26 May (when there were 3067 new cases).

“The claim that immunity levels will hit around 50% by Christmas is not based on any robust analysis of data, and seems more like a finger in the air prediction. Immunity is a complex process and we cannot assume people’s immunity will fade at a uniform rate over time.

“However other, more robust data from other studies shows that while double vaccinated individuals are well protected against infection, and even better protected against serious disease, their level of immunity differs between individuals, and does dissipate over time. This is a reminder that we cannot rely on vaccines alone to prevent the spread of Covid. Lessons from countries like Israel, where the majority of the population were vaccinated early in 2021, shows that a new wave of infections, driven by new more infectious variants, can still drive up infection rates quickly.”