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                                                                     EXHIBIT 5.1

                             WHITE & MCDERMOTT, P.C.
                          65 William Street, Suite 209
                               Wellesley, MA 02181


                                February 17, 1998


Novavax, Inc.
8320 Guilford Road
Columbia, MD  21046

Gentlemen:

      We have assisted with the preparation of a Registration Statement on Form
S-3 (the "Registration Statement"), filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended, relating to the
registration of 2,206,350 shares (the "Shares") of common stock, $.01 par value
(the "Common Stock"), of Novavax, Inc. (the "Company") which may be acquired
upon the conversion of the Series A Preferred Stock of the Company (the "Series
A Preferred Stock").

      We have examined the most recent Amendment to the Certificate of
Incorporation and the Restated Certificate of Incorporation, the By-laws of the
Company and all amendments thereto and have examined and relied on originals, or
copies certified to our satisfaction, of such records of meetings, written
actions in lieu of meetings, or resolutions adopted at meetings, of the
directors of the Company, and such other documents and instruments as in our
judgment are necessary or appropriate to enable us to render the opinions
expressed below.

      In our examination of the foregoing documents, we have assumed (i) the
genuineness of all signatures and the authenticity of all documents submitted to
us as originals, (ii) the conformity to original documents of all documents
submitted to us as certified or photostatic copies and (iii) the authenticity of
the originals of the latter documents.

      Based upon and subject to the foregoing, we are of the opinion that (i)
the shares of Series A Preferred Stock have been duly and validly authorized
and issued and are fully paid and non-assessable and (ii) upon conversion of
the Series A Preferred Stock in accordance with the terms of the Series A
Preferred Stock, and the issuance of the Shares by the Company upon such
conversion, the Shares will be fully paid and non-assessable.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the prospectus forming a part of the Registration Statement.


                                    Very truly yours,

                                    White & McDermott, P.C.


                                    By: /s/ David A. White
                                        --------------------------
                                            David A. White
