Analysis of anti-SARS-CoV-2 Omicron-neutralizing antibody titers in different vaccinated and unvaccinated convalescent plasma sources

The latest SARS-CoV-2 variant of concern Omicron, with its immune escape from therapeutic anti-Spike monoclonal antibodies and WA-1 vaccine-elicited sera, demonstrates the continued relevance of COVID-19 convalescent plasma (CCP) therapies. Lessons learnt from previous usage of CCP suggests focusing on early outpatients and immunocompromised recipients, with high neutralizing antibody titer units. Here, we systematically review Omicron-neutralizing plasma activity data, and report that approximately 47% (424/902) of CCP samples from unvaccinated pre-Omicron donors neutralizes Omicron BA.1 with a very low geometric mean of geometric mean titers for 50% neutralization GM(GMT(50)) of similar to 13, representing a > 20-fold reduction from WA-1 neutralization. Non-convalescent subjects who had received two doses of mRNA vaccines had a GM(GMT50) for Omicron BA.1 neutralization of similar to 27. However, plasma from vaccinees recovering from either previous pre-Omicron variants of concern infection, Omicron BA.1 infection, or third-dose uninfected vaccinees was nearly 100% neutralizing against Omicron BA.1, BA.2 and BA.4/5 with GM(GMT((50))) all over 189, 10 times higher than pre-Omicron CCP. Fully vaccinated and post-BA.1 plasma (Vax-CCP) had a GM(GMT(50)) > 450 for BA.4/5 and >1,500 for BA.1 and BA.2. These findings have implications for both CCP stocks collected in prior pandemic periods and for future plans to restart CCP collections. Thus, Vax-CCP provides an effective tool to combat ongoing variants that escape therapeutic monoclonal antibodies.

Automated summary

The study suggests that convalescent plasma has a high neutralizing effect against the Omicron variant, while vaccinated individuals also show good neutralizing effects. These findings have implications for both previous CCP stocks and future plans to restart CCP collections.