The first study to analyze the structure of the novel coronavirus from two waves of infection in a major city found that a more contagious strain dominates recent samples, researchers from Houston Methodist Hospital said on Wednesday. .... study has not yet been reviewed by outside experts … But they found little evidence that mutations in the virus have made it deadlier, noting that severity of COVID-19, the disease caused by the virus, was more strongly linked to patients’ underlying medical conditions and genetics.