US-based biotechnology company Moderna on Wednesday announced that it has started human trials of an mRNA-based flu shot.The pharmaceutical giant said the first participants have been dosed in the Phase 1/2 study of mRNA-1010, the company's quadrivalent seasonal influenza mRNA vaccine candidate."We are pleased to have begun this Phase 1/2 study of mRNA-1010, our first mRNA seasonal flu vaccine candidate to enter the clinic," Stephane Bancel, Chief Executive Officer of Moderna, said in a statement."We expect that our seasonal influenza vaccine candidates will be an important component of our future combination respiratory vaccines," Bancel added.This Phase 1/2 randomised, stratified, observer-blind, dose-ranging study will evaluate the safety, reactogenicity and immunogenicity of mRNA-1010, Moderna's seasonal influenza vaccine candidate in healthy adults 18 years and older in the US.The company said it intends to enroll approximately 180 participants in the study.mRNA-1010 is Moderna's first seasonal influenza vaccine candidate to enter the clinic and targets lineages recommended by the World Health Organization (WHO) for the prevention of influenza, including seasonal influenza A H1N1, H3N2 and influenza B Yamagata and Victoria.Seasonal flu (type A and type B) epidemics occur seasonally and vary in severity each year, causing respiratory illnesses and placing a substantial burden on healthcare systems.The WHO estimates approximately 3-5 million severe cases of flu each year globally, and 290,000 to 650,000 flu-related respiratory deaths.Approximately 8 per cent of the US population experiences symptoms from flu each year. In the US, the estimated average economic burden of flu is approximately $11 billion per year.