SARS-CoV-2 variants of concern are associated with lower RT-PCR amplification cycles between January and March 2021 in France

•SARS-CoV-2 variants replaced the wild type in France between January and March 2021•The Alpha variant is associated with a 40% increase in transmission on average•The mean transmission advantage of the Beta/Gamma variants is estimated to 28%•Infections by SARS-CoV-2 Alpha, Beta and Gamma variants exhibit lower Ct values•These results suggest these variants have a double viral load compared to wild type