News Release

Clinical results with AVANT rotavirus vaccine demonstrate nearly 90% protection in young children

Peer-Reviewed Publication

Kureczka/Martin Associates

NEEDHAM, MA (July 22, 1999): AVANT Immunotherapeutics, Inc. (Nasdaq: AVAN) announced today the publication of the detailed results of a Phase II clinical study of AVANT's investigational rotavirus vaccine in the British medical journal, Lancet. The results of the Phase II efficacy trial suggests that the two-dose oral rotavirus vaccine should be helpful in the prevention of rotavirus disease in young children. The clinical investigators reported that the vaccine provided those treated with nearly 90% protection from disease.

David Bernstein, M.D., the lead investigator at the Cincinnati Children's Hospital Medical Center, in association with his colleagues at The Johns Hopkins University Medical School in Baltimore, and the Pittsburgh Pediatric Research and Pennridge Pediatric Associates in Philadelphia, examined the effectiveness of the AVANT vaccine in infants.

The authors write, "The efficacy of the two-dose 89-12 vaccine reported in this study, 89% against any rotavirus illness, is the highest reported for any multicenter study. This compares to efficacy for the currently approved three-dose vaccine that ranged from 49% to 68%." They also write, "The 89-12 rotavirus vaccine was safe, immunogenic, and provided a high level of protection against rotavirus disease."

Dr. Bernstein commented, "We were very pleased with the high level of protection provided by AVANT's vaccine. The excellent safety and efficacy data reported in this publication, along with the inherent advantages of this vaccine, indicate that further development of this highly effective rotavirus vaccine is warranted."

The double-blind, placebo-controlled Phase II study involved a total of 215 infants, of ages nine to 16 weeks. Infants received two oral doses of vaccine or placebo and were followed by active surveillance through one rotavirus season. In the reported study, rotavirus disease occurred in only two patients in the vaccine group compared to 18 patients in the placebo group. Side effects were minimal with a significant increase only in mild, transient fever after the first dose (19% vs. 5%) and no significant increase in gastrointestinal symptoms.

AVANT has licensed the oral rotavirus vaccine to SmithKline Beecham (NYSE: SBH) for subsequent development and commercialization. "The rotavirus vaccine provides a significant opportunity for AVANT, through its collaborator SmithKline Beecham, to develop a highly effective vaccine for the prevention of this disease in infants" said Una S. Ryan, Ph.D., President and Chief Executive Officer of AVANT. "We are delighted that the vaccine appears to be so promising at this time."

Rotavirus is a major cause of acute diarrhea and dehydration in infants, which, in the absence of appropriate treatment, can rapidly lead to death. Approximately 500,000 affected infants in the United States require medical treatment annually, with 10-15% requiring hospitalization. Worldwide, rotavirus infection is thought to cause about one million deaths annually, mostly in developing countries. The Centers for Disease Control has recommended universal administration of rotavirus vaccination in children.

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AVANT Immunotherapeutics, Inc. is engaged in the discovery, development and commercialization of products that harness the human immune response to prevent and treat disease. The Company's lead therapeutic program is focused on compounds that inhibit the inappropriate activity of the complement cascade which is a vital part of the body's immune defense system. The Company is also engaged in the development of TheraporeO, a novel system for the delivery of immunotherapeutics for chronic viral infections and certain cancers. The Company and its collaborators are developing vaccines using the proprietary adjuvants, Adjumer and Micromer, for the prevention of influenza, Lyme disease, and respiratory syncytial virus (RSV). In a further collaboration, the Company is developing an oral human rotavirus vaccine, and is developing its own proprietary vaccine for the management of atherosclerosis.

Additional information on AVANT Immunotherapeutics, Inc. can be obtained through the Company's site on the world wide web: http://www.avantimmune.com.

Safe Harbor Statement Under the Private Securities Litigation Reform Act of 1995: This release includes forward-looking statements which reflect AVANT's current views with respect to future events and financial performance. The words "believe," "expect," "anticipate," and similar expressions identify forward-looking statements. Investors should not rely on forward-looking statements because they are subject to a variety of risks, uncertainties, and other factors that could cause actual results to differ materially from those expressed in any such forward-looking statements. These factors include, but are not limited to: (1) the ability to successfully complete development and commercialization of products, including the cost, scope and results of preclinical and clinical testing; (2) the ability to successfully complete product research and further development, including animal, pre-clinical and clinical studies; (3) changes in existing and potential relationships with corporate collaborators; (4) the time, cost and uncertainty of obtaining regulatory approvals; (5) the ability to obtain substantial additional funding; (6) the ability to develop and commercialize products before competitors; and (7) other factors detailed from time to time in filings with the Securities and Exchange Commission.

Contacts:

Una S. Ryan, Ph.D.
President and CEO
AVANT Immunotherapeutics, Inc.
781-433-0771

For Media:

Joan Kureczka/Jesse Fisher
J. Kureczka Associates
415-821-2413

Jim Feuer
Children's Hospital Med. Center of Cincinnati
513-636-7151



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