https://www.sciencedirect.com/science/article/pii/S1201971219303285
Flu killed 68,000 people in Italy over 4 seasons from 2013-2017, or 17,000 a year. With no lockdown measures, quarantine, etc.
Covid-19 has killed 21,067 already in 6-ish weeks in Italy, with around 600 people still dying each day. With a full lockdown in effect for most of that period.
I’d say it’s either substantially deadlier than seasonal flu, or vastly more infectious. Most likely a combination of the two. Somewhat deadlier, somewhat more infectious.
Seeing as it has killed over 10% of positive cases in Italy, and that’s underestimating deaths substantially according to most research on excess mortality this year (in home deaths from it aren’t being counted as no tests are being done on most of those cases but at home deaths have skyrocketed from yearly averages), there would have to be 50-100x more positive cases out there for it be anywhere near seasonal flu rate of .1-.2%