Updated Effectiveness of Covid-19 Vaccines Against Omicron Variant

The COVID-19 pandemic began since December 2019. Due to widespread vaccination, new recorded COVID-19 cases had declined. However, SARS-CoV-2 has mutated over time, and there had been five SARS-CoV-2 variants of concern (VOC), which caused waves of the pandemic. The Omicron variant emerged in late 2021, and became the dominant strain in the world rapidly. The Omicron variant had more mutations than previous SARSCoV-2 variants, making it become a more immune escape variant. Vaccines designed based on wild-type viral strains were less effective against the Omicron variant. Therefore, booster doses were administered to increase vaccine effectiveness in most countries. Besides the strategy of repeating booster doses against Omicron variant, vaccine companies also developed bivalent mRNA vaccine, including wild type/Omicron BA.1 and wild type/Omicron BA.4/5 vaccine.