EMERYVILLE, Calif., July 23 -- Chiron Corporation (Nasdaq: CHIR) today announced that it has delivered the first one million doses of its Fluvirin(R) influenza vaccine to U.S. distributors in preparation for the upcoming influenza season. The company expects to deliver a total of 52 million doses of Fluvirin to the U.S. market this season through regular shipments over the next few months, including 2 million doses later in the season for a national stockpile held by the U.S. Centers for Disease Control and Prevention (CDC). This record level of supply represents an increase of more than one third compared with Fluvirin deliveries during the last influenza season.

"Chiron is committed to protecting millions of people against influenza by increasing the availability of Fluvirin, and vaccine delivery early in the season is an important step in fulfilling this pledge," said Howard Pien, president and chief executive officer of Chiron. "Last influenza season hit early and hit hard. As a result, people increasingly recognized the value of vaccination and sought it at unprecedented rates, leading to a public health milestone of approximately 83 million Americans immunized against influenza. To meet the growing demand for vaccine, our manufacturing teams have worked hard to increase production to record levels and to deliver the vaccine to market as quickly as possible, allowing people to act early to protect themselves and their families this coming influenza season."

As part of the annual preparation for the influenza season, the U.S. Food and Drug Administration's Center for Biologics Evaluation and Research (CBER) tests samples from each batch of influenza vaccine. Upon passing this regulatory testing step, CBER officially releases the vaccine. CBER has begun this process and released the first million doses of Fluvirin. In the coming days, Chiron will complete its internal release procedures, allowing distributors to begin shipping the vaccines to customers.

According to the CDC, about 10 to 20 percent of the U.S. population contracts influenza each year. Vaccination not only decreases the risk of illness for the vaccine recipient but also helps prevent the spread of the influenza virus and limits its role in the potential development of life-threatening complications. The Advisory Committee on Immunization Practices (ACIP) recommends the initiation of influenza vaccination in September for those at high risk for serious complications.

CDC statistics show that, in an average year in the United States, influenza causes 114,000 hospitalizations and kills 36,000 people, primarily in the over-65 population. Together, influenza and pneumonia are the seventh-leading cause of death in the country, killing more people than any other infectious disease. According to the National Foundation for Infectious Diseases (NFID), the annual direct medical costs of influenza are estimated at as much as $4.6 billion. Total direct and indirect costs, including lost work days, of a severe flu epidemic are at least $12 billion.

About Influenza and Influenza Vaccines Influenza, a contagious disease caused by the influenza virus, affects the respiratory tract, often resulting in symptoms in the nose, throat and lungs, as well as fever, headache, tiredness and body aches. It can also lead to complications such as pneumonia, bronchitis, or sinus and ear infections or exacerbate chronic conditions.

Influenza vaccination provides protection from influenza within about two weeks of administration and may last for as long as a year. The vaccine protects 70 to 90 percent of vaccinated people from contracting influenza, and vaccinated people who do contract influenza generally develop milder cases than unvaccinated people. Influenza vaccines, the majority of which are made from inactivated (killed) influenza strains, are updated each year to address changes in the viruses. People who are allergic to eggs, who have had a severe reaction to an influenza shot in the past, or who have previously developed Guillain-Barre syndrome in the six weeks after receiving an influenza vaccination should consult their doctors before receiving influenza vaccination.

Important Safety Information for Fluvirin(R) Influenza Vaccine

The most common side effect of vaccination with Fluvirin is soreness at the injection site. Less common side effects include fever, malaise, myalgia and allergic reactions. Fluvirin should not be administered to anyone with a history of hypersensitivity to any component of the vaccine, including eggs, egg products or thimerosal. As is the case with most drugs and vaccines, there is a chance that a serious allergic reaction, serious illness or even death could occur as a result of vaccination with Fluvirin. Generally, persons should not be vaccinated during an acute febrile illness. Persons should consult with their healthcare providers if they are pregnant and/or are taking other medications. Fluvirin may not protect 100 percent of individuals who are susceptible to influenza. Before administering Fluvirin, please see full prescribing information.

About Chiron

Through its global Blood Testing, Vaccines and BioPharmaceuticals businesses, Chiron Corporation addresses human suffering with more than 50 diverse products to detect, prevent and treat disease worldwide. The company's consistent success has come from its pioneering science, skill in delivering innovations in biotechnology and disciplined business approach.

Chiron believes that science has the power to improve people's lives and harnesses that power to transform human health. For more information about Chiron, please visit http://www.chiron.com.

About Chiron Vaccines

Chiron Vaccines, the world's fifth-largest vaccines business, is headquartered in Oxford, United Kingdom, and has facilities located throughout Europe, the United States and Asia. Chiron Vaccines is the world's second-largest manufacturer of influenza vaccines and has important meningitis, pediatric and travel vaccine franchises. Chiron Vaccines is the leading vaccine manufacturer in the United Kingdom, Germany and Italy. The company's portfolio of products includes vaccines for influenza, meningitis C, rabies, tick-borne encephalitis, yellow fever, haemophilus influenzae B (Hib), polio, mumps, measles and rubella (MMR) and diphtheria, tetanus and pertussis (whooping cough).

This year, Chiron Vaccines celebrates 100 years of advancing medicine with the anniversary of two founding companies. In 1904, Emil von Behring and Achille Sclavo independently started companies in Germany and Italy, respectively, dedicated to the research, development and manufacture of vaccines to protect humanity from infectious disease. As the fifth-largest vaccine manufacturer in the world, Chiron remains dedicated to the legacies of von Behring and Sclavo to prevent disease and develop new vaccines to improve human health globally.

This news release contains forward-looking statements, including statements regarding sales growth, product development initiatives and new product marketing, that involve risks and uncertainties and are subject to change. A full discussion of the company's operations and financial condition, including factors that may affect its business and future prospects, is contained in documents the company has filed with the SEC, including the form 10-Q for the quarter ended March 31, 2004, and the form 10-K for the year ended December 31, 2003, and will be contained in all subsequent periodic filings made with the SEC. These documents identify important factors that could cause the company's actual performance to differ from current expectations, including the outcome of clinical trials, regulatory review and approvals, manufacturing capabilities, intellectual property protections and defenses, stock-price and interest-rate volatility, and marketing effectiveness. In particular, there can be no assurance that Chiron will increase sales of existing products, successfully develop and receive approval to market new products, or achieve market acceptance for such new products. In addition, the company may engage in business opportunities, the successful completion of which are subject to certain risks, including shareholder and regulatory approvals and the integration of operations.

Consistent with SEC Regulation FD, we do not undertake an obligation to update the forward-looking information we are giving today.

NOTE: Fluvirin is a trademark of Chiron Corporation.