Moderna boss predicts current vaccines may be less effective against Omicron covid

Stock markets dip as CEO questions efficacy but others move to calm fears about risk of serious illness

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The chief executive of the US drugmaker Moderna has predicted that existing vaccines will be less effective against Omicron than they have been against the Delta coronavirus variant, a comment that sharply lowered global stock markets.

Stephane Bancel said it would take two weeks to get data on how the existing vaccines performed against the new Covid variant and whether it caused severe disease - but it would take several months to tweak vaccines to tackle it.