Britain has approved Novavax's COVID-19 vaccine for use in those 18 years of age and older, the country's medicines regulator said on Thursday, bringing a fifth coronavirus shot to its roster amidst the rapid spread of the Omicron variant.

The vaccine, Nuvaxovid, was approved as a first and second dose as it met the required safety, quality and effectiveness standards, the UK's Medicines and Healthcare products Regulatory Agency (MHRA) said in a statement.

The British approval for Nuvaxovid comes days after the drugmaker filed for U.S. authorization of the vaccine following months of struggles with development and manufacturing problems, and follows a German backing earlier in the day.

Novavax's Nasdaq-listed shares reversed course to trade 3.7% higher at $92.76 in premarket trading by 1146 GMT.

"We are continuing our vital safety work in monitoring the use of all COVID-19 vaccines, to ensure that their benefits in protecting people against COVID-19 disease continue to outweigh any risks," MHRA Chief Executive June Raine said.

Vaccines from AstraZeneca-Oxford, Pfizer-BioNTech , Moderna and Johnson & Johnson have already been approved for use in the country.

"Nuvaxovid will be the first protein-based vaccine option authorized by MHRA as the United Kingdom tackles this next phase of the pandemic," Novavax Chief Executive Stanley Erck said in a statement.

Novavax's vaccine last June was found to be more than 90% effective in a U.S. trial against a variety of variants, including Delta, while early data from December also suggests it would work against Omicron.

Britain and Novavax in 2020 agreed for the supply of 60 million doses of the shot, while also agreeing to collaborate on conducting late-stage trials for the vaccine in the country.

Following the approval by the MHRA, the Joint Committee on Immunisation and Vaccination will release guidelines for the use of the vaccine in Britain's COVID-19 vaccination program.