As filed with the Securities and Exchange Commission on January 16, 2002

                                                    Registration No. 333-74838
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                           ---------------------------

                         POST-EFFECTIVE AMENDMENT NO. 1
                                   ON FORM S-8
                                       TO
                                    FORM S-4
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                           ---------------------------

                                 MEDIMMUNE, INC.
             (Exact name of registrant as specified in its charter)


                                                                         
           DELAWARE                    35 West Watkins Mill Road               52-1555759
 (State or other jurisdiction        Gaithersburg, Maryland 20878           (I.R.S. Employer
     of incorporation or       (Address of Principal Executive Offices)   Identification No.)
        organization)                         (Zip Code)



                     1999 NON-OFFICER EQUITY INCENTIVE PLAN
                INDIVIDUAL STOCK OPTION GRANTS OUTSIDE OF A PLAN
                           1996 EQUITY INCENTIVE PLAN

                                  David M. Mott
                               c/o MedImmune, Inc.
                            35 West Watkins Mill Road
                          Gaithersburg, Maryland 20878
                     (Name and address of agent for service)

   Telephone number, including area code, of agent for service: (301) 417-0770

                                    copy to:

                               Frederick W. Kanner
                                Richard D. Pritz
                              Dewey Ballantine LLP
                           1301 Avenue of the Americas
                            New York, New York 10019
                                 (212) 259-8000

                         ------------------------------







                         CALCULATION OF REGISTRATION FEE

----------------- -------------- -------------- -------------- -------------

Title of          Amount to be   Proposed       Proposed       Amount of
securities to     registered     maximum        maximum        registration
be registered                    offering       aggregate      fee
                                 price per      offering
                                 share(1)       price(1)
----------------- -------------- -------------- -------------- -------------
Common Stock,
par value $0.01   6,530,000        N/A              N/A           N/A (1)
per share         shares
----------------- -------------- -------------- -------------- -------------

(1)  The registration fee with respect to these shares was previously paid in
connection with the filing of Registrant's Registration Statement on S-4
(Registration No. 333-74838) which was declared effective on January 9, 2002.
See Explanatory Note below.



                                EXPLANATORY NOTE

MedImmune, Inc. (the "Registrant") hereby amends its Registration Statement on
Form S-4 (File No. 333-74838), effective on January 9, 2002 (the "Form S-4"), by
filing this Post-Effective Amendment No. 1 on Form S-8 to the Form S-4 (the
"Registration Statement") relating to 6,530,000 shares of Common Stock, $0.01
par value, of the Registrant (the "Common Stock") issuable in connection with
the 1999 Non-Officer Equity Incentive Plan, Individual Stock Option Grants
Outside of a Plan and the 1996 Equity Incentive Plan, all granted by Aviron
(collectively, the "Plans").

On January 15, 2002, pursuant to an Agreement and Plan of Merger dated December
2, 2001 (the "Merger Agreement"), Aviron became a wholly-owned subsidiary of the
Registrant (the "Merger"). As provided in the Merger Agreement, each outstanding
share of common stock, $0.001 par value, of Aviron ("Aviron Common Stock"), was
converted into the right to receive 1.075 shares of the Registrant's Common
Stock.

Pursuant to the Merger Agreement, Aviron and the Registrant have taken such
actions as are necessary such that Aviron Common Stock is no longer issuable
under the Plans. Instead, the Registrant's Common Stock will be issuable under
the Plans in such amounts and at such prices as adjusted pursuant to the Plans
and the Merger Agreement.

This Registration Statement relates to 6,530,000 shares of the Registrant's
Common Stock registered on Form S-4, which were not issued in connection with
the Merger and that are issuable in connection with the Plans.





                                       2


                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

      This Registration Statement on Form S-8 (the "Registration Statement") is
being filed by MedImmune, Inc. (the "Company" or "Registrant") with respect to
the 1999 Non-Officer Equity Incentive Plan, Individual Stock Option Grants
Outside of a Plan, and 1996 Equity Incentive Plan of Aviron (collectively, the
"Plans"), referred to on the cover of this Registration Statement. The
document(s) containing the information required in Part I of this Registration
Statement will be sent or given to each of the participants in the Plans, as
specified by Rule 428(b)(1) promulgated by the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933 (the "Securities
Act"). Such document(s) are not being filed with the Commission but constitute
(together with the documents incorporated by reference into this Registration
Statement pursuant to Item 3 of Part II hereof) a prospectus that meets the
requirements of Section 10(a) of the Securities Act.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

      The following documents heretofore filed with the Commission pursuant to
the Securities Exchange Act of 1934 (the "Exchange Act") are incorporated herein
by reference:

      (a)   The Company's Annual Report on Form 10-K for the year ended December
            31, 2000;

      (b)   The Company's Description of Common Stock and Amended and Restated
            Rights Agreement on Form 8-A dated April 4, 1991 and December 1,
            1998;

      (c)   All other reports filed by the Company pursuant to Section 13(a) or
            15(d) of the Exchange Act since December 31, 2000;

      (d)   The Company's and Aviron's Selected Unaudited Pro Forma Condensed
            Combined Financial Data, pages 10 through 12 of Amendment No. 1
            to Company's Registration Statement on Form S-4 (No. 333-74838)
            filed January 3, 2002; and

      (e)   Aviron's Annual Report on Form 10-K for the year ended December 31,
            2000, Amended Annual Report on Form 10-K for the year ended December
            31, 2000, and Quarterly Reports on Form 10-Q for the quarters ended
            March 31, 2001, June 30, 2001 and September 30, 2001.

      All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing of a
post-effective amendment which indicates that all Common Stock offered hereunder
has been sold or which deregisters all Common Stock then remaining unsold
hereunder shall be deemed to be incorporated by reference herein and to be a
part hereof from the date of filing of such documents. Any statement contained
in a document incorporated or deemed to be incorporated by reference herein
shall be deemed to be modified or superseded for purposes of this Registration
Statement to the extent that a statement contained herein, or in any other
subsequently filed document that also is or is deemed to be incorporated by
reference herein, modifies or supersedes such statement. Any such statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Registration Statement.

ITEM 4. DESCRIPTION OF SECURITIES

      Not applicable.


                                       3


ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL

      Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS

      Subsection (a) of Section 145 of the General Corporation Law of the State
of Delaware (the "DGCL") empowers a corporation to indemnify any person who was
or is a party or who is threatened to be made a party to any threatened, pending
or completed action, suit or proceeding, whether civil, criminal, administrative
or investigative (other than an action by or in the right of the corporation) by
reason of the fact that the person is or was a director, officer, employee or
agent of the corporation, or is or was serving at the request of the corporation
as a director, officer, employee or agent of another corporation, partnership,
joint venture, trust or other enterprise, against expenses (including attorney's
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by the person in connection with such action, suit or proceeding if the
person acted in good faith and in a manner the person reasonably believed to be
in or not opposed to the best interests of the corporation, and, with respect to
any criminal action or proceeding, had no reasonable cause to believe the
person's conduct was unlawful.

      Subsection (b) of Section 145 empowers a corporation to indemnify any
person who was or is a party or is threatened to be made a party to any
threatened, pending or completed action or suit by or in the right of the
corporation to procure a judgment in its favor by reason of the fact that the
person acted in any of the capacities set forth above, against expenses
(including attorney's fees) actually and reasonably incurred by him in
connection with the defense or settlement of such action or suit if the person
acted in good faith and in a manner the person reasonably believed to be in or
not opposed to the best interests of the corporation, except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the corporation
unless and only to the extent that the Court of Chancery or the court in which
such action or suit was brought shall determine upon application that, despite
the adjudication of liability but in view of all the circumstances of the case,
such person is fairly and reasonably entitled to indemnity for such expenses
which the Court of Chancery or such other court shall deem proper.

      Section 145 further provides that to the extent a director or officer of a
corporation has been successful on the merits or otherwise in the defense of any
action, suit or proceeding referred to in subsections (a) and (b) of Section
145, or in defense of any claim, issue or matter therein, he shall be
indemnified against expenses (including attorneys' fees) actually and reasonably
incurred by him in connection therewith; that indemnification provided for by
Section 145 shall not be deemed exclusive of any other rights to which the
indemnified party may be entitled; the indemnification provided for by Section
145 shall, unless otherwise provided when authorized or ratified, continue as to
a person who has ceased to be a director, officer, employee or agent and shall
inure to the benefit of such person's heirs, executors and administrators; and
empowers the corporation to purchase and maintain insurance on behalf of any
person who is or was a director, officer, employee or agent of the corporation,
or is or was serving at the request of the corporation as a director, officer,
employee or agent of another corporation, partnership, joint venture, trust or
other enterprise against any liability asserted against him and incurred by him
in any such capacity, or arising out of his status as such, whether or not the
corporation would have the power to indemnify him against such liabilities under
Section 145.

      MedImmune provides liability insurance for its directors and officers
which provides for coverage against loss from claims made against directors and
officers in their capacity as such, including liabilities under Securities Act
of 1933.

      Section 102(b)(7) of the DGCL provides that a certificate of incorporation
may contain a provision eliminating or limiting the personal liability of a
director to the corporation of its stockholders for monetary damages for breach
of fiduciary duty as a director, provided that such provision shall not
eliminate or limit the liability of a director (i) for any breach of the
director's duty of loyalty to the corporation or its stockholders, (ii) for acts
or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) under Section 174 of the DGCL, or (iv) for a
transaction from which the director derived an improper personal benefit.
Article EIGHTH of MedImmune's Certificate of Incorporation limits the liability
of directors to the fullest extent permitted by Section 102(b)(7).


                                       4


ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED

      Not applicable.

ITEM 8. EXHIBITS

      See Index to Exhibits on Page 9.

ITEM 9. UNDERTAKINGS

The undersigned registrant hereby undertakes:

      (a)(1) To file, during any period in which offers or sales are being made,
a post-effective amendment to this registration statement:

                  (i)   To include any prospectus required by Section
                        10(a)(3) of the Securities Act of 1933;

                  (ii)  To reflect in the prospectus any facts or events arising
                        after the effective date of the registration statement
                        (or the most recent post-effective amendment thereof)
                        which, individually or in the aggregate, represent a
                        fundamental change in the information set forth in the
                        registration statement;

                  (iii) To include any material information with respect to the
                        plan of distribution not previously disclosed in the
                        registration statement or any material change to such
                        information in the registration statement;

PROVIDED, HOWEVER, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the registrant pursuant to Section 13 or 15(d) of the Securities
Exchange Act of 1934 that are incorporated by reference in the registration
statement.

            (2) That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

            (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

      (b) That, for purposes of determining any liability under the Securities
Act of 1933, each filing of the registrant's annual report pursuant to Section
13(a) or 15(d) of the Securities Exchange Act of 1934 (and, where applicable,
each filing of an employee benefit plan's annual report pursuant to Section
15(d) of the Securities Exchange Act of 1934) that is incorporated by reference
in the registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

      (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the registrant pursuant to the foregoing provisions, or otherwise,
the registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act of
1933 and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the registrant will, unless in
the opinion of its counsel the matter has been settled


                                       5


by controlling precedent, submit to a court of appropriate jurisdiction the
question whether such indemnification by it is against public policy as
expressed in the Securities Act of 1933 and will be governed by the final
adjudication of such issue.



                                       6




                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Gaithersburg, State of Maryland, on the 16th day of
January, 2002.

                                    MEDIMMUNE, INC.



                                    By:       /s/ DAVID M. MOTT
                                        ---------------------------------
                                                  David M. Mott
                                           Chief Executive Officer and
                                            Vice Chairman of the Board

      Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities and on the dates indicated.




                   SIGNATURE                                      TITLE                              DATE

                                                                                          

------------------------------------------------  Chairman of the Board and the
           Wayne T. Hockmeyer, Ph.D.                  Executive Committee


                       *                          Chief Executive Officer and
------------------------------------------------      Vice Chairman of the Board                January 16, 2002
                 David M. Mott                        (Principal Executive Officer)


                       *
------------------------------------------------  President, Chief Operating Officer            January 16, 2002
                Melvin D. Booth                       and Director

                                                  Senior Vice President and Chief
                       *                              Financial Officer
------------------------------------------------      (Principal Financial Officer and          January 16, 2002
               Gregory S. Patrick                     Principal Accounting Officer)

                       *
------------------------------------------------  Executive Vice President,                     January 16, 2002
           Franklin H. Top, Jr., M.D.                 Medical Director and Director

                       *
------------------------------------------------                                                January 16, 2002
            M. James Barrett, Ph.D.               Director

                       *
------------------------------------------------
           James H. Cavanaugh, Ph.D.              Director                                      January 16, 2002


------------------------------------------------
            Barbara Hackman Franklin              Director



                                       7



                                                                                          

                       *
------------------------------------------------                                                January 16, 2002
                Lawrence C. Hoff                  Director


                       *
------------------------------------------------
               Gordon S. Macklin                  Director                                      January 16, 2002



*By:  /s/ DAVID M. MOTT
      ---------------------------------------
      David M. Mott, ATTORNEY-IN-FACT







                                       8




                                INDEX TO EXHIBITS

NUMBER

3.1         Restated Certificate of Incorporation of the Registrant
            (incorporated herein by reference to Exhibit 3.1 to
            Registrant's Annual Report on Form 10-K for the year ended
            December 31, 2000).

3.2         Bylaws of the Registrant (incorporated herein by reference to
            Exhibits 3.2 and 3.3 to Registrant's Annual Report on Form 10-K
            for the year ended December 31, 2000).

4.1         Aviron 1999 Non-Officer Equity Incentive Plan (incorporated herein
            by reference to Aviron's Registration Statement on Form S-8 (File
            No. 333-72120) filed with the Securities and Exchange Commission on
            October 23, 2001).

4.2         Aviron Individual Stock Option Grants Outside of a Plan
            (incorporated herein by reference to Aviron's Registration Statement
            on Form S-8 (File No. 333-44350) filed with the Securities and
            Exchange Commission on August 23, 2000).

4.3         Aviron 1996 Equity Incentive Plan (incorporated herein by reference
            to Aviron's Registration Statement on Form S-8 (File No. 333-44350)
            filed with the Securities and Exchange Commission on August 23,
            2000).

5.1         Opinion of Dewey Ballantine LLP.*

23.1        Consent of Dewey Ballantine LLP (contained in opinion filed as
            Exhibit 5.1).

23.2        Consent of PricewaterhouseCoopers LLP.*

23.3        Consent of Ernst & Young LLP as to Aviron.*

23.4        Consent of Ernst & Young LLP as to U.S. Bioscience, Inc.*

24          Power of Attorney (included on signature page).

--------------
* Filed herewith.



                                       9