13D Filing: Baker Bros. Advisors and Idera Pharmaceuticals Inc. (IDRA)

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

 

SCHEDULE 13D

 

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)*

Idera Pharmaceuticals, Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

45168K306

(CUSIP number)

Alexandra A. Toohey

Chief Financial Officer

Baker Bros. Advisors LP

860 Washington Street, 3^rd Floor

New York, NY 10014

(212) 339-5690

(Name,
address and telephone number of person authorized to receive notices and communications)

October 25, 2017

(Date of event which requires filing of
this statement)

If
the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule
13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box ¨.

(Continued on the following pages)

(Page 1 of 10 Pages)

* The remainder of this cover page
shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover
page.

The information required on the remainder of this cover page
shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise
subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the
Notes).