The green light for the use of redesigned Omicron Covid boosters will enable millions of the retooled shots to roll out as part of a nationwide revaccination campaign.

It accuses them of copying technology that Moderna developed years before the pandemic.

It is the second modified jab that the European Medicines Agency has begun studying for approval after Pfizer-BioNTech's earlier this week.

Even though Moderna's vaccine has proven less effective against the Omicron variant, it remains very good at protecting against severe cases of the disease, the FDA says.

In the study, which did not measure vaccine effectiveness, the booster raised virus-neutralising antibodies by eight-fold against Omicron.

Switzerland, which has ended public health measures designed to curb the spread of the disease, secured a total 34 million doses of Covid-19 vaccines for 2022 for a population of around 8.7 million.

The drugmaker says the contamination was found in just one vial, and it was recalling the whole lot out of 'an abundance of caution'.

Moderna and Gavi have agreements for up to 650 million doses of the company's vaccine to be made available to Covax participants through 2021 and 2022.

Vaccine efficacy in children six months to two years was 43.7%, and vaccine efficacy was 37.5% in the two to under six years age group.

The request comes days after Pfizer-BioNTech, makers of the other Covid mRNA vaccine, also requested emergency approval for a second booster shot, but their request was limited to adults aged 65 and older.

The vaccine is only allowed for adults over feared side effects.

Moderna says preliminary data show antibody response to Omicron at the 50 microgram dose increased 37-fold – but when the dose was doubled, antibody levels increased 83-fold.