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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 SIGA PHARMACEUTICALS, INC --------------------------- (Name of Issuer) COMMON STOCK ----------------------------- (Title of Class of Securities) 826917106 -------------- (CUSIP Number) February 10, 1998 -------------------------- (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: [ ] Rule 13d-1(b) [X] Rule 13d-1(c) [ ] Rule 13d-1(d) - ---------- *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 the disclosures provided in a prior cover page. The information required in 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 ("Act") 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). - ----------------------- --------------------- CUSIP NO. 826917106 13G Page 2 of 5 Pages - ----------------------- --------------------- - ---------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON MedImmune, Inc. I.R.S. #52-1555759 - ---------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [ ] - ---------------------------------------------------------------------------- 3 SEC USE ONLY - ---------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION State of Delaware - ---------------------------------------------------------------------------- NUMBER OF 5 SOLE VOTING POWER SHARES BENEFICIALLY 335,530 OWNED BY EACH REPORTING PERSON WITH --------------------------------------------------- 6 SHARED VOTING POWER -0- --------------------------------------------------- 7 SOLE DISPOSITIVE POWER 335,530 --------------------------------------------------- 8 SHARED DISPOSITIVE POWER -0- - ---------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 335,530 - ---------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES - ---------------------------------------------------------------------------- 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 5.3% - ---------------------------------------------------------------------------- 12 TYPE OF REPORTING PERSON CO - ---------------------------------------------------------------------------- Item 1(a) NAME OF ISSUER SIGA Pharmaceuticals, Inc. Item 1(b) ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICE 666 Third Avenue New York, New York 10017 Item 2(a) NAME OF PERSON FILING MedImmune, Inc. Item 2(b) ADDRESS OF PRINCIPAL BUSINESS OFFICE 35 West Watkins Mill Road Gaithersburg, Maryland 20878 Item 2(c) CITIZENSHIP Delaware Item 2(d) TITLE OF CLASS OF SECURITIES Common Stock Item 2(e) CUSIP NUMBER 826917106 Item 3 IF THIS STATEMENT IS FILED PURSUANT TO RULES 13d-1(b) OR 13d- 2(b), CHECK WHETHER THE PERSON FILING IS A: (a) [ ] Broker or Dealer registered under Section 15 of the Act (b) [ ] Bank as defined in Section 3(a)(6) of the Act (c) [ ] Insurance Company as defined in Section 3(a)(19) of the Act (d) [ ] Investment Company registered under Section 8 of the Investment Company Act of 1940 (e) [ ] An Investment Adviser in accordance with Section 240.13d-1(b)(1)(ii)(E) (f) [ ] An employee benefit plan or endowment fund in accordance with Section 240.13d-1(b)(1)(ii)(F) (g) [ ] A parent holding company or control person in accordance with Section 240.13d-1(b)(ii)(G) (h) [ ] A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (i) [ ] A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (j) [ ] Group, in accordance with Section 240.13d-1(b)(1)(ii)(J) If this Statement is filed pursuant to Section 240.13d- 1(c), check this box. [X] Item 4 OWNERSHIP (see cover page) Item 5 OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [ ]. Item 6 OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON Not applicable Item 7 IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY Not applicable Item 8 IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP Not applicable Item 9 NOTICE OF DISSOLUTION OF GROUP Not applicable Item 10 CERTIFICATION By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect. SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. Dated: February 23, 1998 MEDIMMUNE, INC. By: /s/DAVID LEBUHN Name: DAVID LEBUHN Title: TREASURER