Exhibit 23.1
CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM
We hereby consent to the incorporation by reference in this Registration Statement on FormS-3 of Arsanis, Inc. of our report dated March 9, 2018 relating to the financial statements of Arsanis, Inc., which appears in Arsanis, Inc.’s Annual Report onForm 10-K for the year ended December 31, 2017. We also consent to the reference to us under the heading “Experts” in such Registration Statement.
/s/ PricewaterhouseCoopers LLP
Boston, Massachusetts
January 25, 2019