1

                                                                    EXHIBIT 99.1

AVIRON SUBMITS BIOLOGICS LICENSE APPLICATION FOR FLUMIST(TM)

INNOVATIVE NASAL MIST FLU VACCINE TO BE CO-PROMOTED WITH AMERICAN HOME PRODUCTS
UPON FDA APPROVAL

MOUNTAIN VIEW, Calif. and MADISON, N.J., Oct. 31 /PRNewswire/ -- Aviron (Nasdaq:
AVIR - news) and American Home Products Corporation (NYSE: AHP - news) today
announced that a Biologics License Application (BLA) for FluMist(TM), an
investigational intranasal influenza vaccine, has been submitted to the U.S.
Food and Drug Administration (FDA). Aviron is seeking U.S. licensure of
FluMist(TM) to prevent influenza in children and adults. (Photo:
http://www.newscom.com/cgi-bin/prnh/20001031/SFTU109 )

"Today's BLA submission marks an important milestone in our progress toward
bringing a new influenza vaccine to physicians and patients in the U.S.," said
C. Boyd Clarke, Aviron president and chief executive officer. "We look forward
to continuing to work closely with the FDA throughout the regulatory process."

According to the Centers for Disease Control and Prevention, influenza is a
highly infectious respiratory illness that can cause disease in all age groups.
Annual influenza epidemics in the United States typically affect 10-20 percent
of the general population and cause 20,000 deaths. FluMist(TM), which is
delivered as a gentle nasal mist, could be an important new way to protect
people from the flu. FluMist(TM) may be particularly significant for children,
who suffer high influenza attack rates and are thought to be important in the
spread of influenza.

"The impact of influenza has been a long-standing problem in the United States,"
said Kevin Reilly, president, Wyeth Lederle Vaccines, the vaccine division of
American Home Products Corporation. "We hope this new approach can become an
important tool in the fight against a common infectious disease."

In 1999, Aviron and Wyeth Lederle Vaccines announced a global collaboration
agreement for FluMist(TM).

Aviron is a biopharmaceutical company based in Mountain View, California,
focused on the prevention of disease through innovative vaccine technology.

Wyeth Lederle Vaccines is the vaccine business of Wyeth-Ayerst Laboratories.
Wyeth-Ayerst Laboratories, a division of American Home Products Corporation, is
a major research-oriented pharmaceutical company with leading products in the
areas of women's health care, cardiovascular therapies, central nervous system
drugs, anti-inflammatory agents, infectious disease, hemophilia, oncology,
vaccines, and generic pharmaceuticals. American Home Products Corporation is one
of the world's largest research-based pharmaceutical and health care products
companies. It is a leader in the discovery, development, manufacturing and
marketing of


   2

prescription drugs and over-the-counter medications. It is also a leader in
vaccines, biotechnology, and animal health care.

Actual results may differ materially from the forward-looking statements
contained in this release. Factors that could cause actual results to differ
include, but are not limited to, the assessment by regulatory agencies that the
company's license applications for its nasal influenza vaccine are incomplete or
inadequate to approve the product for marketing to one or more target
populations. Additional information concerning factors that could cause such a
difference is contained in Aviron's SEC filings, including its S-3 Registration
Statement and Annual Report on Form 10-K for the year ended December 31, 1999.

To receive an index and copies of recent press releases, call Aviron's
News-On-Call toll-free fax service, 800-758-5804, extension 114000. Additional
information about the company can be located at http://www.aviron.com.

In conjunction with this news release, Aviron will host a conference call that
will be broadcast live over the Internet. The conference call will take place on
Wednesday, November 1, beginning at 8:30 a.m. EST. To access the webcast, visit
the Aviron Web site at http://www.aviron.com and log-on to the audio feed as
instructed. If you are unable to participate during the live webcast, the call
will be archived at http://www.aviron.com. The information provided on the
conference call and on the webcast is only accurate at the time of the call, and
Aviron will take no responsibility for providing updated information.


                                       2