Three weeks into 2018, deal activity in the biotech sector is already almost halfway to what it was in 2017, at least in terms of size.

In the early hours of Monday morning, French drug giant Sanofi said it would buy hemophilia drugmaker Bioverativ, a Biogen spinout that is less than a year old, for $11.6 billion. Hours later, cancer drugmaker Celgene announced a deal for its partner, Juno Therapeutics, for $9 billion.

A pickup in M&A activity is always a bull thesis for biotech investors, especially after what Jefferies analyst Michael Yee called "a relatively lackluster year for biopharma M&A" in 2017.

There were only 12 public deals last year, for a total value of $50 billion, Yee wrote in a research note last week — and a large portion of that was made up of J&J's $30 billion purchase of Swiss biotech Actelion.

Will deals, as biotech investors perennially hope, beget more deals? Biotech investors seem to think so, boosting the IBB biotech ETF by more than 2 percent Monday, and the XBI (in which both Bioverativ and Juno are among the heaviest-weighted stocks) by 3.5 percent. Cue the matchmaking.