The US Centres for Disease Control and Prevention (CDC) has said three US studies show that a third dose of an mRNA vaccine is key to fighting the Omicron coronavirus variant, providing 90 per cent protection against hospitalisation due to Covid-19.

The studies, led by the CDC, are among the first in the United States to look at the impact of booster doses against the fast-spreading Omicron variant, which now accounts for 99pc of all new Covid cases.

Overall, they suggest that boosters helped protect against both infection and symptomatic disease. Adults aged 50 and older saw the most benefit from an extra dose of the vaccines made by BioNTech SE with Pfizer Inc or Moderna Inc.

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