Orbimed Advisors SC 13G/A Xenon Pharmaceuticals / ORBIMED ADVISORS ownership change

CUSIP No.  98420N105  SCHEDULE 13G Page 8 of 8 Pages

EXHIBIT A

JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on this Schedule 13G dated February 12, 2021 (the “Schedule 13G”), with respect to the Common Stock, without par value, of Xenon Pharmaceuticals Inc. is filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, and that this Agreement shall be included as an Exhibit to this Schedule 13G. Each of the undersigned agrees to be responsible for the timely filing of the Schedule 13G, and for the completeness and accuracy of the information concerning itself contained therein. This Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned have executed this Agreement as of February 12, 2021.

OrbiMed Advisors LLC
By:	/s/ Jonathan T. Silverstein
	Name:	Jonathan T. Silverstein
	Title:	Member
By:	/s/ Sven H. Borho
	Name:	Sven H. Borho
	Title:	Member
By:	/s/ Carl L. Gordon
	Name:	Carl L. Gordon
	Title:	Member
OrbiMed Capital LLC
By:	/s/ Jonathan T. Silverstein
	Name:	Jonathan T. Silverstein
	Title:	Member
By:	/s/ Sven H. Borho
	Name:	Sven H. Borho
	Title:	Member
By:	/s/ Carl L. Gordon
	Name:	Carl L. Gordon
	Title:	Member