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Connda

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The Lancet Microbe
Jul 2021 Vol 2, Number 7, e279
COVID-19 vaccine efficacy and effectiveness—the elephant (not) in the room
Piero Olliaro,Els Torreele,Michel Vaillant

"Vaccine efficacy is generally reported as a relative risk reduction (RRR). It uses the relative risk (RR)—ie, the ratio of attack rates with and without a vaccine—which is expressed as 1–RR. Ranking by reported efficacy gives relative risk reductions of
95% for the Pfizer–BioNTech,
94% for the Moderna–NIH,
91% for the Gamaleya,
67% for the J&J,
and 67% for the AstraZeneca–Oxford vaccines.

However, RRR should be seen against the background risk of being infected and becoming ill with COVID-19, which varies between populations and over time.  Although the RRR considers only participants who could benefit from the vaccine, the absolute risk reduction (ARR), which is the difference between attack rates with and without a vaccine, considers the whole population.
ARRs tend to be ignored because they give a much less impressive effect size than RRRs:
1·3% for the AstraZeneca–Oxford,
1·2% for the Moderna–NIH,
1·2% for the J&J,
0·93% for the Gamaleya
and 0·84% for the Pfizer–BioNTech vaccines.

(HTML) https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00069-0/fulltext
(PDF) https://www.thelancet.com/pdfs/journals/lanmic/PIIS2666-5247(21)00069-0.pdf

Unfortunately this article is being misinterpreted and used in social media to make erroneous claims about vaccine efficacy.

 

REUTERS: Fact Check: Why Relative Risk Reduction, not Absolute Risk Reduction, is most often used in calculating vaccine efficacy

 

"Referring to a “peer reviewed study” published in medical journal The Lancet, users on social media have erroneously claimed that the reported efficacy rates for the available COVID-19 vaccines are “deceiving” and that the real rate of protection from immunization is much lower.

 

"posts erroneously claim the article was a “peer reviewed study”, when it was actually a commentary by Piero Olliaro, Els Torreele and Michel Vaillant on April 20, featured in the Lancet Microbe."

 

"When asked about the claim, Olliaro, professor of poverty related infectious diseases at the Centre for Tropical Medicine and Global Health of Oxford University ( here ) told Reuters via email it was “extremely disappointing to see how information can be twisted.”

 

The Reuter's article presents a full explanation.

 

It's possible for a vaccine to have 100% efficacy yet have an ARR of just 1%.