WASHINGTON, United States (AFP) — The US Food and Drug Administration on Tuesday released a positively-worded briefing document about the Moderna COVID-19 vaccine, a strong sign that a group of experts that meets in two days could vote to approve it.

The agency said there were “no specific safety concerns identified that would preclude issuance of an EUA (emergency use authorisation” and confirmed an overall efficacy of 94.1 per cent.

Rollout of the Pfizer-BioNTech vaccine began on Monday and if the FDA convened panel green lights Moderna’s, its distribution could start as early as next week. 

It comes as more than 300,000 people have died from the virus in the US, and cases continue to surge across much of the country.

The FDA document offered the clearest look yet into the Moderna vaccine, which was co-developed with the National Institutes of Health.

It showed the two-dose regimen protected younger people slightly better than it did older people.

In a clinical trial of 30,400 people, 196 fell ill with COVID-19 by November 21 —  11 in the vaccine group and 185 in the placebo group.

Efficacy was 95.6 per cent for people aged 18-65; 86.4 per cent among those aged 65 and older; and 94.1 per cent overall.

Importantly, of 30 cases of severe COVID-19, all occurred in the placebo group.

The FDA also looked at detailed safety data, at a median of nine weeks after participants had received the second shot, which is taken 28 days after the first.

– Cutting edge technology –

The most common side effects associated with the drug, called mRNA-1273, were injection site pain in roughly 90 per cent of cases; fatigue in 70 per cent, headache in 60 per cent, muscle pain in 60 per cent, joint pain in 45 per cent and chills in 45 per cent.

Few of these effects were classed as “severe” and when they were that tended to occur more in the young than in the old. 

Lymphadenopathy, or swollen lymph nodes occurred in 1.1 per cent of the vaccine group compared to 0.6 per cent of the placebo group.

There was an imbalance in “hypersensitivity” events —  which refers to allergic or inflammatory reactions by the immune system —  which occurred in 1.5 per cent of the vaccinated population compared to 1.1 per cent of the non-vaccinated.

But there were none that were classed as severe or anaphylactic.

Throughout the follow-up period to date, there have been three reports of Bell’s palsy —  a facial paralysis condition —  in the vaccine group and one in the placebo group.

The Pfizer trial saw four people get Bell’s palsy in the vaccine group, and none in the placebo group.

In both cases, the FDA said there was insufficient information to determine that the vaccine was the cause of this paralysis, which normally resolves within three months.

The frequency of serious events which would be considered life-threatening were low, around one per cent in each group, and there was no suggestion that the vaccine was the cause.

Both the Pfizer and Moderna vaccines use a cutting-edge technology based on mRNA (messenger ribonucleic acid) which makes the human cells they enter express a surface protein of the new coronavirus.

This simulates an infection and trains the immune system to be ready in case it encounters the real virus. 

The US hopes to immunise 20 million people this month, with health care workers and long-term case residents at the front of the line. 

Authorities want to reach the rest of the population by summer, but much will depend on vaccine confidence. Experts estimate more than 70 per cent of people will need to be vaccinated to bring the outbreak to a close.