All adults in the UK aged over 50 have now been offered a first dose of a coronavirus vaccine.

It means the Government has met its target of offering the jab to all of its top nine priority groups, including the clinically vulnerable and health and social care workers, three days ahead of its target date of April 15.

The Joint Committee on Vaccine and Immunisation will shortly set out its final advice for the completion of the programme, expected to begin this week with those in their late 40s.

NHS patients in England are also set to receive the Moderna Covid-19 vaccine from today.

It becomes the third vaccine - after Pfizer and AstraZeneca - to be rolled out in the country. 

So here is everything you need to know about it:

How effective is it against coronavirus?

The phase three results suggested vaccine efficacy against the disease was 94.1%, and vaccine efficacy against severe Covid-19 was 100%.

More than 30,000 people in the US took part in the trial, from a wide range of age groups and ethnic backgrounds.

Two doses were given 28 days apart so researchers could evaluate safety and any reaction to the vaccine.

Who developed the vaccine?

Moderna is a US pharmaceutical and biotechnology company with its headquarters in Cambridge, Massachusetts.

The vaccine received funding from two US federal agencies – the National Institute of Allergy and Infectious Diseases (NIAID) and the Biomedical Advanced Research and Development Authority (Barda).

Dolly Parton is credited with helping fund the jab after donating one million dollars (about £716,000) to Vanderbilt University Medical Centre in Nashville, Tennessee, which participated in the research.

How many doses of Moderna does the UK have?

The Government has bought 17 million doses – enough to vaccinate about 8.5 million people.

A benefit of the Moderna vaccine is that it can be safely stored at temperatures of around minus 20C (minus 4F) – achievable in a standard pharmaceutical fridge – making distribution much easier.

The Pfizer vaccine on the other hand has to be stored at minus 70C (minus 94F) and is only stable for a short period at higher temperatures, making it difficult to administer away from hospital hubs.

The Moderna jab can be stored for about 30 days before use.

Is the vaccine safe and what are the side effects?

Moderna has said the vaccine was generally well tolerated, with no serious safety concerns identified.

Severe events after the first dose included injection-site pain, and after the second dose included fatigue, myalgia (muscle pain), arthralgia (joint pain), headache, other pain and redness at the injection site.

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But these were generally short-lived.

Like all medicines, the vaccine can cause possible side effects – but not everyone gets them.

Common side effects with the Moderna vaccine can include flu-like symptoms and pain or swelling at the injection site, most can be treated by paracetamol.

Is the Moderna vaccine effective against variants?

In late January, the company behind the vaccine said it was effective against both the strain first detected in south east England and the mutation which first emerged in South Africa.

Moderna said laboratory tests found no significant impact on antibodies against the UK variant relative to prior variants.

While there was a six-fold reduction in neutralising antibodies produced against the South African variant, the levels remained above those that are expected to be protective, Moderna said.