mRNA-1273 and BNT162b2 mRNA vaccines have reduced neutralizing activity against the SARS-CoV-2 Omicron variant

The SARS-CoV-2 Omicron variant emerged in November 2021 and consists of several mutations within the spike. We used a live virus neutralization assay to examine the neutralizing activity of the Omicron against mRNA vaccine-induced antibody responses. Following 2-4 weeks after primary series of vaccinations, we observed a 30-fold reduction in neutralizing activity against Omicron. Six months after the initial two vaccine doses, sera from naïve vaccinated subjects showed no neutralizing activity against the Omicron. In contrast, COVID-19 recovered individuals six months after receiving the primary series of vaccinations show a 22-fold reduction with majority of the subjects retaining neutralizing antibody responses. In naïve individuals following a booster shot (3rd dose), we observed a 14-fold reduction in neutralizing activity against Omicron and over 90% of subjects show neutralizing activity. These findings show that a 3rd dose is required to provide robust neutralizing antibody responses against the Omicron variant.严重急性呼吸综合征冠状病毒2型（SARS-CoV-2）奥密克戎变异株于2021年11月出现，其刺突蛋白（spike）携带多处突变。本研究采用活病毒中和试验，检测奥密克戎株针对mRNA（messenger RNA）疫苗诱导抗体应答的中和活性。在完成基础免疫程序后的2至4周，我们观测到针对奥密克戎株的中和活性下降30倍。在完成初始两剂疫苗接种后的6个月，未感染过新冠的疫苗接种者血清无法检测到针对奥密克戎株的中和活性。与之形成对比的是，已感染新冠并完成基础免疫程序的个体在接种6个月后，其中和活性仅下降22倍，且绝大多数受试者仍保留中和抗体应答。对于完成加强针（第3剂）接种的未感染新冠个体，我们观测到其针对奥密克戎株的中和活性下降14倍，但仍有超过90%的受试者可检测到中和活性。上述研究结果表明，需接种第3剂疫苗方可诱导出针对奥密克戎变异株的强效中和抗体应答。