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All UK adults are to be offered the booster jab by the end of January, Prime Minister Boris Johnson has announced.

This is in response to a new Covid-19 variant arriving in the UK, known as the Omicron variant.

The news came on the day that stricter rules on face masks also came into force in England.

Face masks are now once again required to be worn in shops and on public transport and secondary schools in England have been "strongly advised" to reintroduce mask wearing in shared areas.

All adults will be offered the booster jab, three months after their second dose of the vaccine, which is earlier than was originally planned.

Boris Johnson said the reason this change is needed, is to stop the spread of the new Omicron variant of coronavirus.

A total of 22 cases of the new variant have so far been confirmed in the UK.

Finding a new variant of Covid-19 isn't unusual. The virus is constantly changing and adapting to its surroundings, so lots of strains have been discovered since we first came across the disease.

The reason rules are changing as a result of this new Omicron strain, is because scientists don't know enough about it yet, and the Prime Minister says that putting these measures in place will allow us to be in the best possible position if there was an increase in infection.

The Prime Minister added that booster jabs would be prioritised in order of age, with older adults being offered the vaccine first.

Almost 18 million people in the UK have already had a booster jab.

Yesterday, Government advisers recommended that all children aged 12 to 15 in the UK should be offered a second dose of a Covid vaccine, although the final decision on these Covid measures lies with politicians.

There are no plans to vaccinate children under the age of 12 at the moment.