Moderna’s vaccine could be the second to be authorised in the US, following that of Pfizer/BioNTech © AFP via Getty Images

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The US health regulator has found Moderna’s coronavirus vaccine to be safe and “highly effective”, clearing the way for a second jab to receive emergency use authorisation later this week.

The Food and Drug Administration report on Tuesday on Moderna’s vaccine trials suggested that immunity began about 10 days after the first of two injections, much like the one made by Pfizer and BioNTech, which received emergency use authorisation last week.

A second approval could significantly expand access to Covid-19 vaccines in the US, where the pandemic has now killed more than 300,000 people, according to Johns Hopkins University data. While the US government has offered to help Pfizer expand manufacturing capacity, it secured another pre-order for 100m Moderna vaccines last week, bringing its total to 200m.

The FDA report said: “The two-dose vaccination regimen was highly effective in preventing PCR-confirmed Covid-19 occurring at least 14 days after receipt of the second dose.”

After both jabs, the vaccine was 94.1 per cent effective in a trial of about 30,000 participants. The shot was less effective in people over the age of 65, with an efficacy rate of 86.4 per cent. There were 30 severe cases of Covid-19 in the placebo group but none in the vaccinated group. There were no deaths from Covid-19 in either group.

Line charts showing cumulative incidence rates for the Pfizer and Moderna Covid-19 vaccines and placebos

Moderna’s vaccine may also be the first to show some impact on asymptomatic infections, according to a document submitted by the company after its original application. According to Moderna, just 14 people who received the vaccine during a clinical trial tested positive for Covid-19 but did not show symptoms, compared with 38 participants who only received a placebo.

So far, all the vaccines have focused on stopping people from developing the Covid-19 disease. But if a vaccine can also stop the initial infection, it could help control the spread of the virus from person to person. People who get infected can spread the virus before they show symptoms — and about 30 to 40 per cent never show symptoms at all.

The report will now be examined by an outside panel of experts, who will give a recommendation on Thursday on whether to approve the vaccine on an emergency basis for people aged 18 and older. The FDA will then give its final decision.

Moncef Slaoui, Donald Trump’s vaccine tsar, said on Monday he expected Moderna’s vaccine to be authorised this week. 

Moderna’s vaccine is based on the same messenger ribonucleic acid, or mRNA, technology as the Pfizer/BioNTech vaccine. A genetic code to the virus’ spike protein is delivered into the body in a bubble of fat, to teach the immune system to respond to the virus.

FDA scientists said there were no specific safety concerns that should prevent emergency authorisation. But they said there is not enough evidence for how the vaccine works in under-18s and pregnant and breastfeeding women, who were not included in the trials.

The most common side effects for the Moderna vaccine were pain at the injection site, fatigue and headache. There were no cases of allergic reactions, as has been seen in two participants in the Pfizer vaccination programme in the UK.

There were also cases of potential side effects that were similar to that seen in Pfizer’s data.

Three vaccinated participants experienced Bell’s palsy, a weakness of muscles in the face, compared with one in the placebo group. One of the cases was considered serious, as a woman had to be hospitalised for a stroke because of new facial paralysis 32 days after the vaccination, although that is now resolving. The scientists cannot draw a causal link between the vaccine and the condition.

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