There are concerns whether current antibody treatments and vaccines will remain effective against the Omicron variant. Using sequence analysis and protein models of the viral spike protein, the Omicron spike protein was found to have 37 mutations from the Wuhan-Hu-1 spike protein, 13 of which were unique to Omicron. This spike protein is important as antibodies target this protein to neutralize the virus. By measuring the activity of virus-encoded luciferase in cell lysates, Hoffmann et al. examined the ability of different clinical interventions to induce antibody-mediated neutralization of Omicron. Omicron was fully resistant against the casirivimab and imdevimab monoclonal antibody cocktail and the etesevimab and bamlanivimab monoclonal antibody cocktail, indicating resistance against many current COVID-19 therapies. Only soluble ACE2 and the monocolonal antibody of sotrovimab were active against the Omicron spike. Furthermore, based on analysis of 17 patient sera or plasma collected within two months of mild or severe COVID-19 symptoms, convalescent antibodies had 44-fold less efficiency in neutralization of the Omicron spike compared to the Delta spike. This indicates that convalescent patients might not be protected against reinfection with Omicron. Regarding COVID-19 vaccines, the study analysed 30 sera collected 14 to 72 days after administration of the individual’s last dose. Two doses of BioNTech-Pfizer vaccine had 12-fold less efficiency in neutralization of the Omicron spike compared to Delta. However, three doses of the BioNTech-Pfizer vaccine resulted in two-fold reduced efficiency compared to Delta. Heterologous vaccination with a first dose of Astra Zeneca-Oxford and a second dose of BioNTech-Pfizer resulted in neutralization of Omicron only 3-fold less efficient than Delta.