Low vaccination rates among schoolchildren and NHS workers are feared to be partially driving a “mutant” strain of flu across the UK.

Some schools have been forced to close temporarily because so many pupils and teachers are off sick, while at least one hospital declared a critical incident on Monday.

NHS leaders have warned people eligible for the flu jab to take up the offer, amid predictions that the outbreak could peak over the Christmas break. New Feature

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The current strain sweeping through the UK is H3N2, also known as subclade K, which is a mutation of the influenza A virus and is believed to be behind an earlier than normal outbreak this season .

Hospitals with highest numbers of flu patients

Official figures show that in

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