Current evidence on efficacy of COVID‐19 booster dose vaccination against the Omicron variant: A systematic review

Coronavirus disease 2019 (COVID-19) is an ongoing pandemic, which affected around 45 million confirmed cases of COVID-19, including more than 6 million deaths. However, on November 24, 2021, the World Health Organization announced a new severe acute respiratory syndrome coronavirus 2 variant designated as the B.1.1.529, a variant of concern (VOC), and the variant has been named as "Omicron." Available preliminary evidence suggests that, as compared with previous VOCs, it has an increased risk of infectivity. Studies have shown that protection from various vaccines effectiveness against hospitalization and death from severe COVID-19 disease is decreasing slowly after a two-dose schedule of COVID-19 vaccines. In…