Vaccines, Blood & Biologics

H5N1 Influenza Virus Vaccine, manufactured by Sanofi Pasteur, Inc. Questions and Answers

On April 17, 2007, FDA licensed the first vaccine in the United States for the prevention of H5N1 influenza, commonly referred to as avian influenza or "bird flu." This inactivated influenza virus vaccine is for use in people 18 through 64 years of age who are at increased risk of exposure to the H5N1 influenza virus subtype contained in the vaccine. This vaccine is derived from the A/Vietnam/1203/2004 influenza virus. The vaccine is manufactured by Sanofi Pasteur Inc. of Swiftwater, PA and has been purchased by the federal government for inclusion within the Nation's National Stockpile.

This vaccine could be used in the event that the H5N1 avian influenza virus develops the capability to spread efficiently from person to person, resulting in the rapid spread of disease across the globe. Vaccines are critical to help counter the spread of influenza disease during a pandemic.



Questions about H5N1 Influenza Virus and Vaccine

What is avian influenza?

Avian influenza - the "bird flu" - is a virus that infects birds, particularly wild birds such as ducks and geese, but can spread to domestic poultry, such as chickens and turkeys. There are numerous different strains of avian influenza; however, most do not cause illness in people. H5N1 is a strain of avian influenza, and is a concern among the scientific and medical community with regard to its potential to cause a pandemic. The H5N1 strain can infect birds, other animals and people.

What is an influenza pandemic?

An influenza pandemic is a global outbreak of disease that occurs when a new influenza virus appears in the human population, causes serious illness, and spreads easily from person to person. It can sweep across a country and around the world in a very short time. People have little immunity to the virus that causes a pandemic. Like seasonal influenza many people get every year, pandemic influenza will probably spread by infected people coughing or sneezing or by touching something with the influenza virus on it and then touching their mouth or nose. An influenza pandemic will likely cause more severe illness, even death, and affect more people than seasonal influenza.

The H5N1 strain of the avian influenza virus has caused the largest number of reported cases of severe disease and death in humans of any avian influenza viruses and is a potential candidate for starting the next pandemic.

Wherever and whenever an influenza pandemic starts, everyone around the world is at risk for getting the disease.

Has anyone in the United States been diagnosed with avian influenza?

No cases of avian influenza occurring in people have been reported in the United States or North America, but there have been cases in other parts of the world such as Asia Africa, and the Middle East. According to statistics provided by the World Health Organization, from 2003 through February 2013, there have been 620 laboratory-confirmed cases in humans, of whom, 367 died. Each additional case provides the virus an opportunity to improve its ability for human-to-human transmission and develop into a pandemic strain.

Is H5N1 avian influenza more serious than seasonal influenza?

Yes. H5N1 avian influenza has some of the standard seasonal influenza symptoms such as high fever, headache, and muscle aches, but people quickly become seriously ill and pneumonia, difficulty breathing, and multi-organ failure have been common among people who have become infected with H5N1 influenza.

How well does the vaccine manufactured by Sanofi Pasteur work?

One multi-center, randomized, double-blinded, placebo-controlled, dose-ranging study in healthy adults, 18 to 64 years of age, investigated the safety and immunogenicity of the vaccine. A total of 103 healthy adults received a 90 microgram dose of the vaccine by injection, followed by another 90 microgram dose, 28 days later. In addition, there were approximately another 300 healthy adults who received the vaccine at doses lower than 90 micrograms and a total of 48 who received placebo by injection.

Of the various doses tested, the study showed that the 90 microgram dose had the better immune response, meaning that at this particular dose, the vaccine induced the most antibodies in the blood against the H5N1 influenza virus strain. The 90 microgram two-dose regimen produced levels of antibodies expected to reduce the risk of getting H5N1 influenza in 45% of those who received it. Although the remaining individuals did not develop this level of antibody, current scientific information on other influenza vaccines, suggests that less than optimal antibody levels may still have the potential to help reduce disease severity and influenza-related hospitalizations, and deaths.

Why didn't the clinical trial include more people?

FDA recognizes that a limited number of people were studied in the clinical trial. The study was designed by the National Institutes of Health (NIH) as an exploratory study to look at the amount of antibodies generated in people from various doses. Because the results showed promise for providing protection against the H5N1 influenza virus and helping with national preparedness for influenza pandemic, Sanofi Pasteur submitted a Biologics License Application to FDA.

Although each 90 microgram dose required to stimulate the immune response is more than is used in Sanofi-Pasteur’s seasonal influenza vaccine, Fluzone, the manufacturing process and vaccine formulation for their H5N1 vaccine is the same as Fluzone, which has a long record of safety and effectiveness.

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Questions about Adverse Side Effects and Who Should Not be Immunized

What are the risks associated with the vaccine?

The vaccine was generally well-tolerated by the recipients in the study, with pain and tenderness at the injection site, headache, general ill feeling, and muscle pain being the most common complaints. However, because the number of people studied was small, rare safety events may not have been identified, but given the potential risk of a pandemic, which can cause serious illness and death; its benefits outweigh its risks. In addition, Sanofi Pasteur has agreed to work with the U.S. government to gather additional information on the safety and effectiveness of the vaccine should it be used in the event of a pandemic.

How will FDA monitor the safety of a pandemic influenza vaccine if it is used

Once a pandemic influenza vaccine is distributed, the FDA and the Centers for Disease Control and Prevention (CDC) use the Vaccine Adverse Event Reporting System (VAERS) to look for new safety concerns (“safety signals”) which may emerge as many more individuals receive the vaccine. These adverse event safety signals are then evaluated in epidemiological studies to determine whether they are occurring more often than expected in people who receive a vaccine. FDA also examines electronic healthcare records to look for elevated rates of previously identified adverse events that could be related to a pandemic vaccine. In 1976, an elevated rate of Guillain-Barre syndrome, a neurological condition that causes muscle weakness, led to the suspension of a pandemic influenza vaccination campaign. Each year FDA monitors this condition with near real time seasonal influenza vaccine safety surveillance of healthcare data from the Centers for Medicaid & Medicare Services. This program will be adapted for pandemic vaccine monitoring, and surveillance plans for other health outcomes are currently being developed. FDA is also developing the capability to monitor Guillain Barre syndrome and other outcomes using healthcare data that can be accessed by the Post Licensure Rapid Immunization Safety Monitoring program, part of the FDA's Sentinel Initiative.

During the 2009 H1N1 pandemic, FDA and other federal agencies including the Department of Veterans Affairs, Department of Defense, and the CDC contributed to the monitoring the safety of the 2009 H1N1 influenza vaccine and would likely do so for any future pandemic vaccines that are used.

What if a pandemic is declared and the influenza virus strain of the pandemic is different than the influenza virus strain in this vaccine?

No one can predict which influenza virus subtype (strain) will cause the next pandemic. Several factors affect the effectiveness of influenza vaccines. One major factor is the degree to which circulating strains and influenza vaccine strains are similar. If the pandemic virus strain is substantially different from the H5N1 virus contained in the vaccine, it is unlikely that the existing vaccine would be effective. If the influenza pandemic strain turns out not to be a perfect match with the vaccine strain, it does not necessarily mean that the vaccine can't be used; studies have shown that influenza vaccine may provide some immunity against strains that are somewhat different. However, in the event of a pandemic, licensure of this H5N1 vaccine permits manufacture by Sanofi Pasteur of an H5N1 vaccine well “matched” to the pandemic strain as a strain change supplement – as also occurs with the yearly seasonal vaccine manufacture. It is possible that the next influenza pandemic will be caused by a strain of influenza that does not belong to the H5N1 subtype. This scenario would require development of a new vaccine.

The goal of pandemic preparedness is to develop additional vaccines and vaccination strategies that will be ready for use against various strains that have the potential to cause a pandemic.

Does the vaccine contain a preservative?

Yes, thimerosal, a mercury containing compound, is used as a preservative in the vaccine. Because the vaccine is supplied in a multi-dose vial; it is necessary to have a preservative to prevent the growth of bacteria and fungus in the event that the vaccine is accidentally contaminated with repeated puncture of a needle into the multi-dose vials.

Will the vaccine be available to anyone who wants it?

No, the manufacturer has stated that the vaccine won't be available to the public commercially, meaning it can't be obtained from a doctor's office. It has been purchased by the federal government for inclusion within the country's National Stockpile, for distribution by the Department of Health and Human Services in case it is ever needed.

Why is the vaccine for inclusion within the National Stockpile and not being made available to everyone?

The production capacity of the United States currently is not sufficient to make vaccine rapidly available for the entire population. Inclusion of this vaccine in the National Stockpile will ensure that when it is needed, those who are designated as priority recipients, will have vaccine available to them.

Even though it will be in the Stockpile, can people who may be at risk of exposure to H5N1 influenza virus, such as travelers to infected regions of the world, poultry workers, or first-responders get the vaccine?

At this time, immunization is not recommended for populations that may be at risk of exposure to H5N1 influenza virus.

Why does the approved indication not include children or elderly?

It is not uncommon for new vaccines to be tested in a healthy adult population and then once further information is gathered about benefits and risks, additional testing is done in other populations such as children and the elderly.

How is the vaccine administered?

It is administered as a two-dose regimen. One 90 microgram dose is given intramuscularly, in the upper arm, and a second 90 microgram dose is given in the same manner, 28 days later.

Is it possible to become infected with avian influenza from the H5N1 vaccine?

No. The vaccine is made from killed influenza viruses, and they cannot cause influenza infection.

Will the annual influenza vaccine protect people against pandemic influenza?

No, current annual influenza vaccines include influenza viruses to protect against A subtypes H1N1 and H3N2 and B viruses. A vaccine made from these viruses would not provide protection against a different influenza A subtype virus (such as H5N1).

It is important to continue to get vaccinated every year as this is the best way to prevent illness from the seasonal influenza virus.

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For More Information

Where can I get more information on avian influenza and actions that can be taken to prepare for a pandemic?

Information can be found at Flu.gov>. This website provides one-stop access to U.S. Government seasonal and pandemic influenza information and is managed by the Department of Health and Human Services.

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Related Links

Contact FDA

(800) 835-4709
(240) 402-8010
Consumer Affairs Branch (CBER)

Division of Communication and Consumer Affairs

Office of Communication, Outreach and Development

Food and Drug Administration

10903 New Hampshire Avenue

Building 71 Room 3103

Silver Spring, MD 20993-0002

Page Last Updated: 08/12/2013
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