key: cord-0968873-oj75qvjo
authors: Correia, Luis C L; Matias, Denise
title: COVID-19 vaccines: effectiveness and number needed to treat
date: 2021-05-14
journal: Lancet Microbe
DOI: 10.1016/s2666-5247(21)00119-1
sha: d1960c2c0785473fbcea36c27c1f32e359ff88bb
doc_id: 968873
cord_uid: oj75qvjo

nan

First, number needed to treat (NNT) is not an intrinsic property of a treatment, it is rather a property of the population that receives a treatment: for a constant relative risk reduction, populations of different baseline risks will have different absolute reductions. Therefore, NNT comparison of different treatments across studies should be avoided, because sample populations will always have baseline risk variations. Indeed, this approach is the actual reporting bias.

Second, the authors raise a concern that different levels of background risk might change relative risk reduction of studies. This statement disregards the constant property of relative risk repeatedly demonstrated by subgroup analysis of clinical trials and meta-scientific evaluations of a treatment across studies of different baseline risks. 2 For example, statins, 3, 4 anti-hypertensive therapy, 5 and aspirin 6 have the same relative risk reduction across the baseline risks of primary or secondary prevention.

Finally, effectiveness-a real-world property-is about clinical decision making, and not to be derived from efficacy studies (randomised controlled studies). As a clinician or an epidemiologist, one should multiply the RRR (intrinsic property of a treatment) by the baseline risk of a given population or patient, individualising the ARR and NNT. They are not scientific concepts, they are circumstantial information.

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