ROTARIX Vaccine Approved by Mexican Authorities for the Prevention of Severe Gastroenteritis in Infants

July 19, 2004

AVANT Immunotherapeutics, Inc (Nasdaq: AVAN) today reported that its partner, GlaxoSmithKline (GSK) announced that the Board of Health in Mexico have approved the Rotarix(R) vaccine for marketing in Mexico for the prevention of gastroenteritis caused by rotavirus infection. Rotarix(R) has been in development at GSK Biologicals since 1997 when it was in-licensed from AVANT.

"We are delighted to announce this initial approval for Rotarix(R), which marks a significant event for AVANT - the first commercial approval of a human healthcare product from AVANT's extensive portfolio of advanced vaccines," said Una S. Ryan, AVANT President and Chief Executive Officer. "It also marks an important advance in the fight against rotavirus disease, a major cause of serious illness and mortality in infants for much of the world."

Rotavirus infection is the leading cause of severe diarrhea and vomiting in infants and young children between 3-24 months world-wide. If untreated, the virus can rapidly kill, as the sickest children become dehydrated from 10 to 20 episodes of diarrhea in a single day. Globally, rotaviruses account for approximately 138 million cases of infantile gastroenteritis each year and it was recently reported that rotavirus is responsible for approximately 440,000 deaths per year, a child a minute, the majority of which occur in the Indian subcontinent, sub-Saharan Africa and South America.

Rotarix(R) is an oral, two-dose, live attenuated vaccine developed from a single human strain designed to provide broad protection against multiple rotavirus strains and to provide early protection before the onset of rotavirus illness. The vaccine works by stimulating the body to mimic the immune response to natural rotavirus infection, which protects against the subsequent development of moderate to severe rotavirus disease.

More than 70,000 infants have been enrolled in the global clinical development program, with studies conducted in Europe, the US, Latin America and Asia to evaluate the safety and efficacy of Rotarix(R). These studies demonstrate that Rotarix(R) is an effective, safe and well-tolerated vaccine.

Rotarix(R) has shown up to 90% efficacy against severe rotavirus-related gastroenteritis in the first year of life, as defined by the well established and widely used Vesikari 20-point scale, and up to 84% efficacy in the second year of life against severe rotavirus-related gastroenteritis. In addition, Rotarix(R) was 86% effective in preventing hospitalizations due to rotavirus-related gastroenteritis. Rotarix(R) has demonstrated protection against different circulating strains of rotavirus when compared to the original strain of the vaccine.

Rotarix(R) has demonstrated a side effect profile similar to that of a placebo vaccine with only limited reactogenicity observed. To date, there is no evidence of an increased risk of intussusception. An Independent Data Safety Monitoring Board (IDSMB), which monitors the safety aspects of the Rotarix(R) clinical development program, is reviewing the data on an ongoing basis.

"We are delighted that Mexico has become the first country in the world to approve Rotarix(R), an important new vaccine to prevent severe rotavirus-related gastro-enteritis in infants worldwide," said Jean Stephenne, President and General Manager of GSK Biologicals.