Intended for healthcare professionals


Covid-19: Protection from two doses of vaccine wanes within six months, data suggest

BMJ 2021; 374 doi: (Published 25 August 2021) Cite this as: BMJ 2021;374:n2113

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  1. Gareth Iacobucci
  1. The BMJ

Protection provided by two doses of the Pfizer and the AstraZeneca covid-19 vaccines wanes within six months, an analysis of UK data suggests.

The latest analysis from the Zoe Covid Study, which investigates real world vaccine effectiveness, examined data from positive PCR test results between May and July 2021 among 1.2 million people who had received two doses of Pfizer or AstraZeneca vaccine.

The results, released in a press release, show that protection after two doses of the Pfizer vaccine decreased from 88% at one month to 74% at five to six months; protection for AstraZeneca decreased was from 77% at one month to 67% at four to five months.

Tim Spector, lead scientist on the Zoe Covid study app, said that the findings showed the need to assess whether booster doses might be required for some groups. “In my opinion, a reasonable worst case scenario could see protection below 50% for elderly people and healthcare workers by winter,” he said. “If there are high levels of infection in the UK, driven by loosened social restrictions and a highly transmissible variant, this scenario could mean increased hospitalisations and deaths. We urgently need to make plans for vaccine boosters and decide if a strategy to vaccinate children is sensible.”

The follow-up analysis, which has not been peer reviewed, examined self-reported side effects of vaccination in people using the Zoe Covid Symptom Study app, using the same methods as a study published in Lancet Infectious Diseases on 27 April.1 It used data from vaccines logged from 8 Dec 2020 to 13 Jul 2021 and from infections that occurred between 26 May 2021, when the delta variant (B.1.617.2) became dominant, and 31 Jul 2021.

Commenting on the results, Ian Jones, professor of virology at the University of Reading, said, “Waning immunity has been a concern since the start of the epidemic, based on data from the commonly circulating coronaviruses. To date, however, the studies that have followed vaccination have been a bit more sanguine, suggesting the fall off in antibody titre may be slower than first supposed. This latest study confirms that a decline is happening, but it is not yet clear what this means for disease severity, the key aspect of protection afforded by the vaccines.

“The worst case scenario suggested is certainly possible, but a better case scenario would be that, even at 50% protection from infection, protection from disease remains robust and hospital numbers remain manageable. The need for boosters still needs to be balanced with global vaccine distribution to populations where even a first shot will lower virus circulation, and with it the chance of future variants.”

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