Regeneron Pharmaceuticals Inc's Covid-19 antibody treatment and other similar drugs could be less effective against the new Omicron coronavirus variant, the company said.

The drugmaker said further analyses are ongoing to confirm and quantify this potential impact using the actual Omicron variant sequence. Regeneron's shares were down 2.8 per cent at $636 before the bell.

Global markets fell on Tuesday following comments from Moderna Inc's chief executive officer, who said Covid-19 vaccines are unlikely to be as effective against Omicron as they have been previously.

Regeneron said analysis shows the individual mutations present in Omicron indicate “there may be reduced neutralisation activity of both vaccine-induced and monoclonal antibody conveyed immunity”. The analysis included Regeneron's Covid-19 antibody cocktail REGEN-COV, according to the company.