Eli Lilly (NYSE:LLY) announced that it had amended purchase agreements with the U.S. government to prioritize using two monoclonal antibodies — bamlanivimab and etesevimab — in tandem.

In March, the U.S. government announced that it would stop using bamlanivimab alone, given its reduced efficacy against some SARS-CoV-2 variants.

But pairing anti-SARS-CoV-2 monoclonal antibodies together can offer more robust protection against variants. Using two of the monoclonal antibodies together is more protective than administering either alone.

The COVID-19 Treatment Guidelines Panel of the National Institutes of Health has recommended pairing Lilly’s bamlanivimab with etesevimab or Regeneron’s (NSDQ:REGN) cocktail combining casirivimab and imdevimab.

Regeneron’s REGEN-COV drug is an antibody cocktail combining casirivimab and imdevimab.

Bamlanivimab and etesevimab have been granted emergency use authorization but have not been approved by FDA.