People who have had their booster vaccine by 11 December will have “very high protection against Covid-19 by Christmas Day”, the Department of Health and Social Care has said.

Research has shown that two weeks after a booster, people have very high level of protection from getting a symptomatic case of Covid-19.

It comes as some of Britain’s biggest charities have backed the booster campaign.

The British Heart Foundation, Cancer Research UK and Diabetes UK are among 16 charities encouraging vulnerable people to take up the offer of a top-up jab.

So far about 16 million people have had a booster vaccine or a third dose across Britain.

People aged 40 and over and the clinically vulnerable are eligible to get a booster six months after their second jab, and they are able to book their appointment after five months has lapsed.

Eligible people are encouraged to get their booster as soon as possible after data showed falling levels of protection from symptomatic disease and hospital admission six months after people have had their second jab.

The charities will also encourage patients to get a flu jab.

Announcing the campaign, a Department spokesperson said: “People who have had their booster vaccine by 11 December will have very high protection against Covid-19 by Christmas Day.

“Following a rise in cases and a return of lockdown restrictions in Europe, those eligible for a booster have been urged to take up the offer as soon as possible to protect themselves, their families and help to reduce the pressure on the NHS.”

A study previously published by the UK Health Security Agency showed in adults aged 50 years and over, protection against symptomatic infection was 93.1% in those whose first two doses were of the Oxford/AstraZeneca jab.

Those who had an initial course of Pfizer saw protection rise to 94%.

Health and Social Care Secretary, Sajid Javid, said: “I am hugely grateful to all the charities who are backing our vaccine campaign and supporting some of the most vulnerable in our society.

“With winter approaching, it’s so important that those who are at risk from the virus are protected in order to keep themselves safe.

“The vaccines are safe and effective and are helping us build a wall of defence against Covid-19. Please come forward for yours as soon as you can.”

The charities taking part in the coalition include: African Caribbean Leukaemia Trust; Anthony Nolan; British Heart Foundation; British Liver Trust; Cancer Research UK; Carers UK; Diabetes UK; Epilepsy Action; Epilepsy Society; Kidney Care UK; Kidney Research UK; Macmillan; Parkinson’s UK; Rethink Mental Illness; Sickle Cell Society; Terrence Higgins Trust.