**EXHIBIT31.1**

**CERTIFICATION:**

I, David M. Mott, certify that:

1.      I have reviewed this annualreport on Form 10-K of MedImmune, Inc.

2.      Based on my knowledge, thisannual report does not contain any untrue statement of a material fact or omitto state a material fact necessary to make the statements made, in light of thecircumstances under which such statements were made, not misleading withrespect to the period covered by this annual report;

3.      Based on my knowledge, thefinancial statements, and other financial information included in this annualreport, fairly present in all material respects the financial condition,results of operations and cash flows of the registrant as of, and for, theperiods presented in this annual report;

4.      The registrant’s othercertifying officer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e)and 15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a)      designed such disclosurecontrols and procedures or caused such disclosure controls and procedures to bedesigned under our supervision to ensure that material information relating tothe registrant, including its consolidated subsidiaries, is made known to us byothers within those entities, particularly during the period in which thisannual report is being prepared;

(b)      designed such internalcontrol over financial reporting, or caused such internal control overfinancial reporting to be designed under our supervision, to provide reasonableassurance regarding the reliability of financial reporting and the preparationof financial statements for external purposed in accordance with generallyaccepting accounting principles;

(c)      evaluated the effectivenessof the registrant’s disclosure controls and procedures as of the end of theperiod covered by this report based on such evaluation; and

(d)      disclosed in this report anychange in the registrant’s internal control over financial reporting thatoccurred during the registrant’s most recent fiscal quarter (the registrant’sfourth fiscal quarter in the case of an annual report) that has materiallyaffected, or is reasonably likely to materially affect, the registrant’sinternal control over financial reporting; and

5.      The registrant’s othercertifying officer and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the registrant’s auditors and theaudit committee of the registrant’s board of directors (or persons performingthe equivalent functions):

(a)      allsignificant deficiencies and material weaknesses in the design or operation ofinternal control over financial reporting which are reasonably likely to adverselyaffect the registrant’s ability to record, process, summarize and reportfinancial information; and

(b)      anyfraud, whether or not material, that involves management or other employees whohave a significant role in the registrant’s internal control over financialreporting.

Date: February 27, 2007
|                |     |     |   | /s/  David M. Mott                                              |
|----------------|----------|----------|--------|----------------------------------------------------------------------|
|      |     |     |   | David M. Mott                                                        |
| *  * | * * | * * |   | *Chief Executive Officer, President and  Vice Chairman of the Board* |

 

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