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Un petit mot bubu sur ces chiffres qui viennent du Lancet  ? 

COVID-19 vaccine efficacy and effectiveness—the elephant (not) in the room 

Piero Olliaro, Els Torreele, Michel Vaillant

The Lancet Microbe, Published : April 20, 2021 DOI :https://doi.org/10.1016/S2666-5247(21)00069-0

ARRs [the absolute risk reduction] tend to be ignored because they give a much less impressive effect size than RRRs : […] 0.84% for the Pfizer–BioNTech vaccine.

ARR is also used to derive an estimate of vaccine effectiveness, which is the number needed to vaccinate (NNV) to prevent one more case of COVID-19 as 1/ARR. NNVs bring a different perspective : 76 for the Moderna–NIH, 78 for the AstraZeneca–Oxford, 80 for the Gamaleya, 84 for the J&J, and 117 for the Pfizer–BioNTech vaccines. The explanation lies in the combination of vaccine efficacy and different background risks of COVID-19 across studies : 0·9% for the Pfizer–BioNTech.

The only reported indication of vaccine effectiveness is the Israeli mass vaccination campaign using the Pfizer–BioNTech product. Although the design and methodology are radically different from the randomised trial,Dagan and colleagues report an RRR of 94%, which is essentially the same as the RRR of the phase 3 trial (95%) but with an ARR of 0·46%, which translates into an NNV of 217 (when the ARR was 0·84% and the NNV was 119 in the phase 3 trial). This means in a real-life setting, 1.8 times more subjects might need to be vaccinated to prevent one more case of COVID-19 than predicted in the corresponding clinical trial.

These considerations on efficacy and effectiveness are based on studies measuring prevention of mild to moderate COVID-19 infection ; they were not designed to conclude on prevention of hospitalisation, severe disease, or death, or on prevention of infection and transmission potential. Assessing the suitability of vaccines must consider all indicators, and involve safety, deployability, availability, and costs.