Document:

<PAGE>   1
                                                                   Exhibit 10.33

                   AMENDMENT NO. 1 TO STOCK TRANSFER AGREEMENT

        THIS AMENDMENT NO. 1 TO STOCK TRANSFER AGREEMENT entered into as of the
16th day of February, 2000, by and among AVIRON, a Delaware corporation
("Company") and the REGENTS OF THE UNIVERSITY OF MICHIGAN ("University").

                                    RECITALS

        WHEREAS, the Company and the University are parties to that certain
Materials Transfer and Intellectual Property Agreement dated February 24, 1995
and that certain Stock Transfer Agreement dated February 24, 1995 (the "Transfer
Agreement").

        WHEREAS, pursuant to Section 5 of the Transfer Agreement, Aviron agreed
to deliver to University a warrant for the purchase of Aviron Common Stock equal
to one and twenty-five one-hundredths percent (1.25%) of the total number of
issued and outstanding shares of the Company's Common Stock on the Issue Date
(as defined therein).

        WHEREAS, the parties desire to amend the Transfer Agreement in order to
issue a warrant as of the date hereof and amend the calculation of the number of
shares to be issued pursuant to the warrant to be issued to the University on
the Issue Date as set forth below.

        NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties agree as follows:

SECTION 1. ISSUANCE OF WARRANT.

        1.1 Promptly upon execution of this Agreement, the Company will issue to
University a warrant to purchase three hundred forty thousand (340,000) shares
of the Company Common Stock at an exercise price per share of Ten Dollars
($10.00) (the "Initial Exercise Price" and the "New Warrant"). The New Warrant
shall be in substantially the form attached as Exhibit B to the Transfer
Agreement, except that: (i) the term of the New Warrant shall be for seven (7)
years from the date hereof; and (ii) the section entitled "Right to Convert
Warrant into Stock," shall be amended so that the University may elect to
convert the entire New Warrant or any portion thereof from time to time during
the term of the New Warrant.

        1.2 The Company represents and warrants that the Initial Exercise Price
is properly calculated according to Section 5.3 of the Transfer Agreement.

        1.3 In the event that the calculation of the Warrant Shares (as defined
in the Transfer Agreement and as amended below), is negative or zero, then
University shall retain the New Warrant and there shall be no adjustment of the
number of shares exercisable under the New Warrant.

        1.4 If the University exercises/converts the Warrant in full or portion
prior to the date of the First Commercial Sale of any Product (as defined in the
Transfer Agreement) and is not able to sell the Warrant Shares pursuant to Rule
144 under the Securities Act of 1933, as

                                       1.
<PAGE>   2

amended, then the Company agrees to register (this agreement is for one such
registration) the Warrant Shares for resale on a Form S-3 Registration Statement
(if such form is available for use by the Company) with the Securities and
Exchange Commission and both parties agree that such registration shall be on
terms and conditions substantially similar to those registration rights granted
to American Home Products Corporation pursuant to Section 5 of that certain
Common Stock Purchase Agreement by and between American Home Products
Corporation and the Company dated February 3, 2000.

SECTION 2. AMENDMENT OF CALCULATION FOR FURTHER ISSUANCE OF WARRANT.

        2.1 The first paragraph of Section 5.2 of the Transfer Agreement is
amended in its entirety as follows:

        "Subject to the provisions of Section 5.4 below, the Warrant shall be
        exercisable for a number of shares of the Company Common Stock (the
        "Warrant Shares") equal to one and twenty-five one-hundredths percent
        (1.25%) of the total number of issued and outstanding shares of the
        Company Common Stock on the Issue Date (including, on an as-converted
        basis, outstanding shares of Preferred Stock of the Company) less three
        hundred forty thousand (340,000) shares of the Company Common Stock (as
        adjusted for recapitalizations, stock splits, dividends and the like).
        If such number is negative or zero then no Warrant shall be issued. For
        purposes of calculating this percentage, "issued and outstanding shares
        of the Company Common Stock" shall NOT include shares of the Company
        Common Stock, or securities convertible into the Company Common Stock:"

        IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO.
1 TO STOCK TRANSFER AGREEMENT as of the date set forth in the first paragraph
hereof.

AVIRON                                 THE REGENTS OF THE
                                       UNIVERSITY OF MICHIGAN

By: /s/ FRED KURLAND                   By: /s/ NORMAN G. HERBERT
   -----------------------------          --------------------------------------
    Fred Kurland
    Senior Vice President and          Name:   Norman G. Herbert
    Chief Financial Officer                 ------------------------------------
                                       Title:  Associate Vice President
                                               and Treasurer
                                             -----------------------------------

                                       By: /s/ L. ERIK LUNDBERG
                                           -------------------------------------

                                       Name:   L. Erik Lundberg
                                            ------------------------------------
                                       Title:  Chief Investment Officer
                                             -----------------------------------

                                       2.<PAGE>   1
                                                                   EXHIBIT 10.40

                            SECURED PROMISSORY NOTE

$335,887.94                                                Date:  March 27, 1998

                                                           Due:   April 1, 2001

FOR VALUE RECEIVED, MachOne Communications, Inc. a California corporation (the
"Borrower") hereby promises to pay to the order of Comdisco, Inc., a Delaware
corporation (the "Lender") at P.O. Box 91744, Chicago, IL 60693 or such other
place of payment as the holder of this Secured Promissory Note (this "Note") may
specify from time to time in writing, in lawful money of the United States of
America, the principal amount of THREE HUNDRED THIRTY-FIVE THOUSAND EIGHT
HUNDRED EIGHTY-SEVEN and 94/100 Dollars ($335,887.94) together with interest at
eight percent (8.0%) per annum from the date of this Note to maturity of each
installment on the principal hereof remaining from time to time unpaid, such
principal and interest to be paid in 36 equal monthly installments of $10,534.80
each, commencing May 1, 1998 and on the same day of each month thereafter to and
including April 1, 2001 and an additional final installment of $50,383.19
("Balloon Payment") to be paid on April 1, 2001, such installments to be applied
first to accrued and unpaid interest and the balance to unpaid principal.
Interest shall be computed on the basis of a year consisting of twelve months of
thirty days each.

This Note is the Note referred to in, and is executed and delivered in
connection with, that certain Loan and Security Agreement of even date herewith
by and between Borrower and Lender (as the same may from time to time be
amended, modified or supplemented in accordance with its terms, the "Loan
Agreement"), and is entitled to the benefit and security of the Loan Agreement
and the other Loan Documents (as defined in the Loan Agreement), to which
reference is made for a statement of all of the terms and conditions thereof.
All terms defined in the Loan Agreement shall have the same definitions when
used herein, unless otherwise defined herein.

The Borrower waives presentment and demand for payment, notice of dishonor,
protest and notice of protest and any other notice as permitted under the UCC or
any applicable law.

                                      -1-
<PAGE>   2
This Note has been negotiated and delivered to Lender and is payable in the
State of Illinois, and shall not become effective until accepted by Lender in
the State of Illinois. This Note shall be governed by and construed and enforced
in accordance with, the laws of the State of Illinois, excluding any conflicts
of law rules or principles that would cause the application of the laws of any
other jurisdiction.

       BORROWER:                   MACHONE COMMUNICATIONS, INC.
                                   992 S. DE ANZA BLVD.
                                   SAN JOSE, CA 95129

                                   Signature:   /s/ [Signature Illegible]
                                             -------------------------------

                                   Print Name:  [Illegible}
                                             -------------------------------

                                   Title:       Secretary
                                             -------------------------------

                                      -2-<PAGE>   1
                                                                   EXHIBIT 10.41

                            SECURED PROMISSORY NOTE

$1,250,000                                               DATE: NOVEMBER 10, 1998

                                                         DUE:  NOVEMBER 1, 2001

FOR VALUE RECEIVED, MachOne Communications, Inc., a California corporation (the
"Borrower") hereby promises to pay to the order of Comdisco, Inc., a Delaware
corporation (the "Lender") at P.O. Box 91744, Chicago, IL 60693 or such other
place of payment as the holder of this Secured Promissory Note (this "Note")
may specify from time to time in writing, in lawful money of the United States
of America, the principal amount of ONE MILLION TWO HUNDRED FIFTY THOUSAND and
00/100 Dollars ($1,250,000) together with interest at Nine percent (9%) per
annum from the date of this Note to maturity of each installment on the
principal hereof remaining from time to time unpaid, such principal and
interest to be paid in 6 equal monthly installments of interest only, the first
monthly installment in the amount of $6,562.50, commencing December 1, 1998,
followed by 5 monthly installments of $9,375.00 each, commencing January 1,
1999 and on the same day of each month thereafter to and including May 1, 1999,
followed by 30 equal monthly installments of principal and interest in the
amount of $46,685.20 each, commencing June 1, 1999 and on the same day of each
month thereafter to and including November 1, 2001 such installments to be
applied first to accrued and unpaid interest and the balance to unpaid
principal. Interest shall be computed on the basis of a year consisting of
twelve months of thirty days each.

This Note is the Note referred to in, and is executed and delivered in
connection with, that certain Loan and Security Agreement dated as of September
10, 1998 by and between Borrower and Lender (as the same may from time to time
be amended, modified or supplemented in accordance with its terms, the "Loan
Agreement"), and is entitled to the benefit and security of the Loan Agreement
and the other Loan Documents (as defined in the Loan Agreement), to which
reference is made for a statement of all of the terms and conditions thereof.
All terms defined in the Loan Agreement shall have the same definitions when
used herein, unless otherwise defined herein.

The Borrower waives presentment and demand for payment, notice of dishonor,
protest and notice of protest and any other notice as permitted under the UCC
or any applicable law.

                                      -1-
<PAGE>   2
This Note has been negotiated and delivered to Lender and is payable in the
State of Illinois, and shall not become effective until accepted by Lender in
the State of Illinois. This Note shall be governed by and construed and enforced
in accordance with, the laws of the State of Illinois, excluding any conflicts
of law rules or principles that would cause the application of the laws of any
other jurisdiction.

          BORROWER:              MACHONE COMMUNICATIONS, INC.
                                 992 SOUTH DE ANZA BLVD.
                                 CUPERTINO, CA 95129

                                 Signature:   /s/ [Signature Illegible]
                                              ---------------------------------

                                 Print Name:  [Illegible]
                                              ---------------------------------

                                 Title:       V.P. Legal & Regulatory Affairs
                                              ---------------------------------

                                      -2-
<PAGE>   3
MACHONE COMMUNICATIONS

Prepared by G. Gillen

Loan Amount:   1,250,000.00
Interest Rate        9.000%
Payment           46,685.20

<TABLE>
<CAPTION>
Payment Number      Date                Principal                     Interest                 Payment                   Balance
--------------      ----                ---------                     ---------               ---------                ------------
<S>                 <C>                 <C>                           <C>                     <C>                      <C>
                    11/10/98                                                                                           1,250,000.00
 1                  12/01/98                 0.00                      6,562.50                6,562.50                1,250,000.00
 2                  01/01/99                 0.00                      9,375.00                9,375.00                1,250,000.00
 3                  02/01/99                 0.00                      9,375.00                9,375.00                1,250,000.00
 4                  03/01/99                 0.00                      9,375.00                9,375.00                1,250,000.00
 5                  04/01/99                 0.00                      9,375.00                9,375.00                1,250,000.00
 6                  05/01/99                 0.00                      9,375.00                9,375.00                1,250,000.00
 7                  06/01/99            37,310.20                      9,375.00               46,685.20                1,212,689.80
 8                  07/01/99            37,590.03                      9,095.17               46,685.20                1,175,099.77
 9                  08/01/99            37,871.95                      8,813.25               46,685.20                1,137,227.82
10                  09/01/99            38,155.99                      8,529.21               46,685.20                1,099,071.83
11                  10/01/99            38,442.16                      8,243.04               46,685.20                1,060,629.66
12                  11/01/99            38,730.48                      7,954.72               46,685.20                1,021,899.19
13                  12/01/99            39,020.96                      7,664.24               46,685.20                  982,878.23
14                  01/01/00            39,313.61                      7,371.59               46,685.20                  943,564.61
15                  02/01/00            39,608.47                      7,076.73               46,685.20                  903,956.15
16                  03/01/00            39,905.53                      6,779.67               46,685.20                  864,050.62
17                  04/01/00            40,204.82                      6,480.38               46,685.20                  823,845.80
18                  05/01/00            40,506.36                      6,178.84               46,685.20                  783,339.44
19                  06/01/00            40,810.16                      5,875.05               46,685.20                  742,529.28
20                  07/01/00            41,116.23                      5,568.97               46,685.20                  701,413.05
21                  08/01/00            41,424.60                      5,260.60               46,685.20                  659,988.45
22                  09/01/00            41,735.29                      4,949.91               46,685.20                  618,253.16
23                  10/01/00            42,048.30                      4,636.90               46,685.20                  576,204.86
24                  11/01/00            42,363.66                      4,321.54               46,685.20                  533,841.20
25                  12/01/00            42,681.39                      4,003.81               46,685.20                  491,159.80
26                  01/01/01            43,001.50                      3,683.70               46,685.20                  448.158.30
27                  02/01/01            43,324.01                      3,361.19               46,685.20                  404,834.29
28                  03/01/01            43,648.94                      3,036.26               46,685.20                  361,185.34
29                  04/01/01            43,976.31                      2,708.89               46,685.20                  317,209.03
30                  05/01/01            44,306.13                      2,379.07               46,685.20                  272.902.90
31                  06/01/01            44,638.43                      2,046.77               46,685.20                  228,264.47
32                  07/01/01            44,973.22                      1,711.98               46,685.20                  183,291.25
33                  08/01/01            45,310.52                      1,374.68               46,685.20                  137,980.74
34                  09/01/01            45,650.35                      1,034.86               46,685.20                   92,330.39
35                  10/01/01            45,992.72                        692.48               46,685.20                   46,337.67
36                  11/01/01            46,337.67                        347.53               46,685.20                       (0.00)

</TABLE>

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