Efficacy and effectiveness of covid-19 vaccine - absolute vs. relative risk reduction.

The unusual conditions under which COVID-19 vaccines have been tested (in particular social distancing, that cannot be maintained for a long time), possibly makes ARR an unreliable "effectiveness predictor" of vaccination at population level. Keywords: Absolute risk reduction; relative risk reduction; COVID-19; vaccine hesitancy EN Absolute risk reduction relative risk reduction COVID-19 vaccine hesitancy 873 875 3 07/19/22 20220701 NES 220701 Over the last few months, there has been a passionate debate within the scientific community on the risks and the benefits of the vaccines against COVID-19 disease. In this regard, we have to take into account that the effect of COVID-19 vaccines has been evaluated over a background of strict preventive measures at population level (social distancing, hand hygiene, mask wearing) that reduced significantly the background incidence rate and, hence, a steep increase in NNV. Nevertheless, what we primarily need to know during this unprecedented pandemic is that vaccines are safe and that mass vaccination will curb viral circulation in the population or, as recently seen after diffusion of Delta and Omicron variants, will reduce severe COVID-19 cases, preventing health services overload. [Extracted from the article]