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The FDA on Wednesday quietly limited the scope of use of another monoclonal antibody for COVID-19 as data emerges showing lower neutralization against the Omicron BA.2 subvariant.

The agency notes that sotrovimab is currently "until further notice," but in a to manufacturer GlaxoSmithKline, the FDA said that sotrovimab is not authorized to treat mild to moderate COVID "likely to have been caused by a non-susceptible SARS-CoV-2 variant based on available information including variant susceptibility to these drugs and regional variant frequency."

Based on from the Department of Health and Human Services (HHS) when limiting other monoclonal antibodies for Omicron, this could apply to areas where a non-susceptible variant has over 80% prevalence.

Until the recent bebtelovimab EUA, sotrovimab had been the lone monoclonal antibody retaining activity against Omicron. Whether it remains sufficiently active against the Omicron subvariant BA.2 is less clear.

A revealed a 16-fold reduction in neutralization against BA.2 versus the Omicron strain, with the agency noting that the "clinical relevance of the 16-fold reduction in susceptibility is unknown."

That data came from a on February 18, funded by sotrovimab developers Vir Biotechnology and GlaxoSmithKline, which found that "a moderate shift in activity (16-fold change in IC₅₀ [half-maximal inhibitory concentration]) was observed for the Omicron BA.2 variant."

A prior pre-print from researchers at Columbia University in New York City showed sotrovimab had a 27-fold reduction in neutralizing activity against BA.2 versus BA.1. Pre-print data from showed similar declines in activity.

In an , Vir said it has sent more data to the FDA for review, including safety data on higher doses of sotrovimab.

"Initial feedback from the FDA question Vir's conclusion that the 500 mg IV dose of sotrovimab retains activity against the BA.2 Omicron subvariant based on Vir's current modeling assumptions, and the FDA has asked for additional data to support Vir's position," the manufacturer wrote.

NIH COVID guidelines currently recommend antiviral nirmatrelvir/ritonavir (Paxlovid) as the top choice for individuals with mild to moderate COVID at high risk of progressing to severe disease.

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