The US Food and Drug Administration (FDA) has revised the authorisations for two monoclonal antibody therapies of Regeneron and Eli Lilly to limit their usage.

The revised authorisation for Eli Lilly and Company’s bamlanivimab plus etesevimab and Regeneron Pharmaceuticals’ REGEN-COV (casirivimab and imdevimab) comes after data showed that these therapies are very unlikely to be active against the omicron variant of the SARS-CoV-2 virus.

According to the FDA, these therapies are limited to only if a patient is ‘likely to have been infected with or exposed to a variant that is susceptible to these treatments’. 

In August last year, the FDA expanded the emergency use authorization (EUA) for Regeneron’s REGEN-COV to prevent Covid-19.

Monoclonal antibodies are proteins made in laboratories to imitate the ability of the immune system to resist pathogens such as the SARS-CoV-2 virus. 

As the virus can mutate gradually, some therapies may not work against specific variants such as omicron. 

The regulatory agency noted that this is the case with the treatments of Lilly and Regeneron.

With the omicron variant spreading rapidly throughout the country, these antibody therapies are currently not authorised for usage in any US states, territories and jurisdictions, the FDA added.

According to data from US Centers for Disease Control and Prevention (CDC), the omicron variant could have been responsible for over 99% of cases in the US as of 15 January. 

In a press statement, the FDA said: “As it’s very unlikely that individuals with Covid-19 seeking care in the region are currently infected with a variant other than omicron, these antibody therapies are not authorised for usage at present.”

The regulatory authority noted that other treatments – Paxlovid, Veklury (remdesivir), Sotrovimab and Molnupiravir – are likely to work against omicron.

Furthermore, these therapies have received FDA authorisation or approval for treating mild-to-moderate Covid-19 patients at increased disease progression risk, including hospitalisation or death.