“Introduction: … In this study, we performed a systematic literature review of studies reporting VE at different time points since vaccine administration to estimate the waning of vaccine protection. We focused this review on the three most distributed COVID-19 vaccines in Western countries as of June 2022 [22]: BNT162b2 (Pfizer-BioNTech COVID-19 vaccine), mRNA-1273 (Moderna COVID-19 vaccine), and ChAdOx1 nCoV-19 (Oxford-AstraZeneca COVID-19 vaccine). We then performed a secondary analysis of the collected data to provide a cohesive picture of the waning rate associated with different vaccine products and quantified VE against SARS-CoV-2 infection and disease at any time from last dose administration, for different numbers of received doses, and different SARS-CoV-2 variants…
Discussion: … The performed analysis highlighted that the effectiveness of vaccination with 2 doses of BNT162b2, mRNA-1273, and ChAdOx1 nCoV-19 against any laboratory confirmed infection with Delta might have been lower than 70% at 9 months from last dose administration, and that the protection provided by a booster dose against Omicron infection rapidly wanes over time (31.5% mean VE at 6 months from administration). We found that the emergence of the Omicron variant reduced the initial effectiveness acquired from the primary vaccination course against symptomatic infection as well (from 76.2%-93.6% to 56.1%-83.6%, depending on the product considered), while increasing the pace of waning of protection. Our mean estimates indicated that at 6 months from the second dose, any considered vaccine has an effectiveness of less than 13% against Omicron symptomatic infection.”