Chiron Delivers FLUVIRIN(R) Influenza Virus Vaccine to U.S. Customers; First Shipments Mark Beginning of 2005-2006 FLUVIRIN Supply.

EMERYVILLE, Calif. -- Chiron Corporation (NASDAQ:CHIR) today announced that it has initiated the first delivery and release of FLUVIRIN(R) influenza virus vaccine to customers in the United States for the 2005-2006 influenza season. The company expects to continue to deliver shipments of FLUVIRIN vaccine throughout October and November and into December.

Chiron has received all necessary approvals from the U.S. Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA) to start supplying FLUVIRIN vaccine to the U.S. market. Continued shipments of FLUVIRIN vaccine will undergo corresponding internal release procedures and standard FDA influenza vaccine lot release procedures.

"The efforts and commitments of many have made it possible for Chiron to restore the supply of FLUVIRIN vaccine in just one year," said Howard Pien, chief executive officer of Chiron. "We are grateful to the government agencies for the expertise they shared as we worked to remediate, and we are proud of our employees for the dedication and perseverance they have shown through both remediation and production. When the MHRA suspended our license a year ago, we set out to implement a systemic, holistic remediation plan, with the goal of coming back within one season and sustaining our supply for the future. In this process, we received close oversight from both the MHRA and the FDA, including seven GMP (good manufacturing practices) inspections. Thanks to these efforts, we are again positioned to help meet the needs of patients, healthcare providers and customers. Successfully achieving license reinstatement and providing FLUVIRIN vaccine to the United States will reestablish Chiron as a trusted supplier of influenza vaccine."

Chiron has not updated its guidance on total FLUVIRIN vaccine doses or 2005 financial results since its second-quarter earnings report on July 27, 2005. The company now expects that the total number of FLUVIRIN vaccine doses it will produce for the 2005-2006 influenza season will be below its previously stated range, due to production delays related to remediation as well as lower production output associated with adaptation to new processes and procedures implemented in remediation. Accordingly, Chiron expects that its financial results for 2005 will be below its previously stated guidance. Chiron expects to have more information on FLUVIRIN vaccine production totals and financial guidance in the weeks ahead.

"This year, Chiron devoted more than half of the normal production season to the implementation of our remediation plan. We are delighted to be back, and we look forward to contributing meaningfully to the influenza vaccine supply this year," said Mr. Pien. "Chiron recognizes the value of influenza vaccines and their important role in public health, not just for the annual flu season but also as the foundation for pandemic preparedness. We are pleased to be able to reiterate our mission to contribute to protecting people against influenza and will strive to provide innovations that could help to deal with the threat of pandemic."

Influenza vaccination is the most effective way to prevent influenza.(1) Although the influenza season can begin earlier, it usually starts in December, peaks in January or February, and continues through March. According to the U.S. Centers for Disease Control and Prevention (CDC), October and November are the primary months for vaccination, and vaccination in December or later is recommended for those who are not vaccinated earlier. Influenza 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.(2)

"By getting vaccinated against flu each fall, you can help protect yourself, your family, and everyone you interact with from the threat of influenza and the associated lost productivity, suffering and mortality," said William Schaffner, M.D., professor and chairman of the Department of Preventive Medicine at Vanderbilt University School of Medicine and member of the board of directors of the National Foundation for Infectious Diseases. "Everyone -- and especially healthcare workers, whose work environments put them at the epicenter of flu transmission -- wants to avoid getting the flu themselves and, even worse, passing it along to those who are more vulnerable.

"From a public health perspective, every flu season is a new opportunity to improve vaccination rates," said Dr. Schaffner. "Beyond the immediate impact of reducing the burden of influenza, increased demand for this valuable product drives manufacturers to increase supply. Every manufacturer's contribution to the nation's vaccines infrastructure makes our country better prepared to deliver a robust supply of this essential tool, both for the prevention of annual influenza and a potential pandemic."

Under current CDC recommendations, people with the highest risk of serious complications from influenza receive priority for flu shots until October 24, 2005. After that date, all people ages 6 months and older will be eligible to receive flu shots. The priority groups include people ages 65 years and over; residents of long-term care facilities; people ages 2 to 64 years old with certain chronic medical conditions; children ages 6 to 23 months old; pregnant women; healthcare professionals who provide direct patient care; and household contacts and caregivers of children younger than 6 months of age. FLUVIRIN vaccine is not indicated for children younger than 4 years of age.

In an average year in the United States, influenza causes more than 200,000 hospitalizations and kills approximately 36,000 people, primarily in the over-65 population.(3) Together, influenza and pneumonia are the seventh leading cause of death in the country, killing more people than any other infectious diseases. The annual direct medical costs of influenza are estimated at $3 billion to $5 billion. Total direct and indirect costs, including lost work days, of a severe flu epidemic are estimated at $12 billion to $14 billion.(4)

About Influenza and Influenza Vaccines

Influenza, a contagious disease caused by the influenza virus, affects the respiratory tract, often resulting in cough, sore throat, runny or stuffy nose, as well as fever (usually high), headache, extreme tiredness and muscle aches. It can also lead to complications such as bacterial pneumonia, dehydration and worsening of chronic medical conditions, such as congestive heart failure, asthma or diabetes. Children may get sinus problems and ear infections.

Influenza vaccination provides protection from influenza within about two weeks of administration. An annual vaccine closely "matched" to the circulating strains of influenza protects about 70 to 90 percent of healthy adults who are vaccinated from contracting influenza, and vaccinated people who do contract influenza generally develop milder cases than those who have not received the vaccine. Among elderly nursing home residents, the flu shot can be 80 percent effective in preventing death from the flu.(5)

Influenza vaccines are updated each year to address changes in the viruses, and "flu shots" are made with inactivated (killed) influenza strains (the nasal vaccine is made with live attenuated influenza strains). The 2005-2006 influenza vaccine contains A/California/7/2004 (H3N2)-like, A/New Caledonia/20/99 (H1N1)-like and B/Shanghai/361/2002-like influenza virus antigens. People who are severely allergic to eggs, who have had a severe reaction to an influenza vaccination 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 Virus Vaccine

The most common side effect of vaccination with FLUVIRIN vaccine is soreness at the injection site. Less common side effects include fever, malaise, myalgia and allergic reactions. FLUVIRIN vaccine 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 vaccine. Generally, persons should not be vaccinated during an acute febrile illness. FLUVIRIN vaccine is not indicated for use in children under the age of 4 years. Persons should consult with their healthcare providers if they are pregnant and/or are taking other medications. FLUVIRIN vaccine may not protect 100 percent of individuals who are susceptible to influenza. Before administering FLUVIRIN vaccine, please see full prescribing information.

(1)CDC, Key Facts About Influenza and the Influenza Vaccine, September 28, 2005, www.cdc.gov/flu/keyfacts.htm

(2)CDC, Morbidity and Mortality Weekly Report, May 28, 2004, 53 (RR-06); 1-40

(3)CDC, Morbidity and Mortality Weekly Report, July 29, 2005, 54 (RR-08); 1-40

(4)Monto, A.S., Epidemiology and Virology of Influenza Illness, The American Journal of Managed Care, March 2000. S255-S264.

(5)CDC, Morbidity and Mortality Weekly Report, May 28, 2004, 53 (RR-06); 1-40

Media Materials

For images and video related to FLUVIRIN(R) influenza virus vaccine, please visit www.thenewsmarket.com/chiron. Journalists may register and download print-quality images and broadcast-standard video from this site at no charge.

About Chiron

Chiron delivers innovative and valuable products to protect human health by advancing pioneering science across the landscape of biotechnology. The company works to deliver on the limitless promise of science and make a positive difference in people's lives. For more information, please visit www.chiron.com.

This news release contains forward-looking statements, including statements regarding supply of FLUVIRIN(R) influenza virus vaccine that Chiron expects to deliver and sell in the 2005-2006 influenza season, timing of delivery of FLUVIRIN, duration of the flu season, regulatory approvals, improvements to manufacturing facilities, product development initiatives, and product marketing, that involve risks and uncertainties and are subject to change. A discussion of the company's operations and financial condition, including factors that may affect its business and future prospects that could cause actual results and developments to differ materially from those expressed or implied by these forward-looking statements, is contained in documents the company has filed with the SEC, including the Form 10-K for the year ended December 31, 2004, and the Form 10-Q for the quarter ended June 30, 2005, 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, among others, additional adverse developments resulting from the previous suspension of Chiron's UK license to manufacture FLUVIRIN vaccine from October 5, 2004, through March 2, 2005, the announcement of such suspension and the litigation and investigations relating to those matters, the outcome of clinical trials, regulatory review and approvals, manufacturing capabilities, intellectual property protections, litigation, marketing effectiveness, and the severity of the 2005-2006 influenza season. In particular, there can be no assurance that additional issues with respect to FLUVIRIN vaccine or Chiron's manufacturing generally will not arise in the future, or additional doses of FLUVIRIN vaccine will satisfy Chiron's internal release procedures and/or FDA influenza vaccine lot release procedures. The company may face additional competition in the influenza market in the future and challenges in distribution arrangements as a result of previous vaccine developments. In addition, the company may engage in business opportunities, the successful completion of which is subject to certain risks, including approval by Novartis AG, regulatory approvals and the integration of operations.

Chiron does not undertake an obligation to update the forward-looking information the company is giving today.

NOTE: FLUVIRIN is a registered trademark of Chiron.