Booster Covid-19 shots significantly restore protection against mild disease caused by the Omicron variant, in part reversing an otherwise steep drop in vaccine effectiveness, the UK Health Security Agency said on Friday.

The early findings from a real-world analysis are some of the earliest data on the protection against Omicron outside of lab studies, which have shown reduced neutralising activity against Omicron.

"These early estimates should be treated with caution but...