A study to analyse the structure of the coronavirus from two waves of infections in a major city found that a more contagious strain dominates recent samples, researchers from Houston Methodist Hospital said on Wednesday.

They studied over 5,000 genomes from viruses found in the earliest phase of the pandemic in Houston and from an ongoing, more recent wave of infections.

The study, which has not yet been reviewed by outside experts, found that nearly all strains in the second wave had a mutation, known as D614G, which has been shown to increase the number of “spikes” on the crown-shaped virus.

The researchers said patients infected with the variant strain had higher amounts of the virus on initial diagnosis. But there was little evidence mutations in the virus have made it deadlier.

Meanwhile in the UK, chancellor Rishi Sunak on Thursday announced another multi-billion-pound package that includes the exchequer picking up parts of the wage bill of all employees until April 2021.

The package includes extension of VAT relief, loans to struggling companies and extension of grants to the self-employed.