President Donald Trump has said a coronavirus vaccine made by Moderna has been approved for use in the US and distribution will start immediately.

It comes after a panel of US Food and Drug Administration (FDA) advisers said the benefits of the vaccine outweighed the risks for those aged 18 and up.

Clinical trials found the vaccine had an efficacy of 94.1% – and 100% against severe Covid-19.

Nobody who was vaccinated with the vaccine, known as mRNA-1273, developed severe coronavirus.

US firm Moderna said the trial results indicate the jab is generally well tolerated with no serious safety concerns.

– How does the Moderna vaccine work?

It works in a similar way to the jab from Pfizer/BioNTech.

Coronavirus is studded with “spike proteins” that it uses to enter human cells. Covid-19 vaccines target this spike protein.

The Moderna and Pfizer vaccines use synthetic messenger RNA (mRNA), a genetic material that contains information about the spike protein.

The vaccines provide the body with instructions to produce a small amount of this protein which, once detected by the immune system, leads to a protective antibody response.

Moderna’s vaccine does not require the same ultracold storage as Pfizer’s and can remain stable at normal fridge temperature for 30 days.

– How effective is it?

Trials on more than 30,000 people in the US have shown the Moderna jab to be 94.5% effective in preventing coronavirus.

While this efficacy may drop over time, scientists have said the vaccine should protect against around nine in 10 cases of Covid-19.

Moderna has not identified any significant safety concerns.

– What about antibodies and T-cells?

The Pfizer, AstraZeneca and Moderna vaccines have been shown to provoke both an antibody and T-cell response.

Antibodies are proteins that bind to the body’s foreign invaders and tell the immune system it needs to take action.

T-cells are a type of white blood cell which hunt down infected cells in the body and destroy them.

Nearly all effective vaccines induce both.

– When will the Moderna vaccine arrive in the UK?

The Government has signed a deal for seven million doses of the Moderna vaccine for the UK.

That is enough for around 3.5 million people, who will each receive two doses.

According to the Government, Moderna is scaling up its European supply chain which means these doses would become available in the UK in the spring at the earliest.

The UK’s Medicines and Healthcare products Regulatory Agency (MHRA) has been conducting a rolling review of the vaccine.

– Can this vaccine help the elderly?

There have been concerns that a Covid-19 vaccine will not work as well on elderly people, much like the annual flu jab.

However, data from Moderna suggests the jab works across all age groups, including the elderly.

The Pfizer jab has also been shown to work effectively in the elderly.