mRNA booster immunization elicits potent neutralizing serum activity against the SARS-CoV-2 Omicron variant

Neutralization of the SARS-CoV-2 Omicron variant is markedly impaired in sera from recipients of two doses of the COVID-19 vaccine BNT162b2 or from convalescent individuals, but is robustly increased in both groups following a booster vaccine dose. The Omicron variant of SARS-CoV-2 is causing a rapid increase in infections across the globe. This new variant of concern carries an unusually high number of mutations in key epitopes of neutralizing antibodies on the viral spike glycoprotein, suggesting potential immune evasion. Here we assessed serum neutralizing capacity in longitudinal cohorts of vaccinated and convalescent individuals, as well as monoclonal antibody activity against Omicron using pseudovirus neutralization assays. We report a near-complete lack of neutralizing activity against Omicron in polyclonal sera from individuals vaccinated with two doses of the BNT162b2 COVID-19 vaccine and from convalescent individuals, as well as resistance to different monoclonal antibodies in clinical use. However, mRNA booster immunizations in vaccinated and convalescent individuals resulted in a significant increase of serum neutralizing activity against Omicron. This study demonstrates that booster immunizations can critically improve the humoral immune response against the Omicron variant.

Automated summary

This study demonstrates that neutralization of the SARS-CoV-2 Omicron variant is greatly reduced in individuals who received two doses of the COVID-19 vaccine or have recovered from the disease, but is significantly increased after a booster vaccine dose.