A study of the Pasteur institute in France seems to indicate that Covid-19 was already silently circulating in France in February, a scenario compatible with the large proportions of mild or asymptomatic diseases and observations in other European countries.
source: https://www.biorxiv.org/content/10.1101/2020.04.24.059576v1.full.pdf & https://www.marianne.net/societe/decouverte-d-une-troisieme-souche-du-covid-19-le-virus-circulait-silencieusement-sur-notre
