Frequently Asked Questions about the Safety of the 2009 H1N1 Influenza Vaccine

Are the 2009 H1N1 influenza vaccines safe?

The 2009 H1N1 vaccines have undergone all the safety testing and quality checks that are usually done for other vaccines. We expect the 2009 H1N1 influenza vaccine to have a similar safety profile as seasonal flu vaccines, which have a very good safety track record. Over the years, hundreds of millions of Americans have received seasonal flu vaccines. The most common side effects following flu vaccinations are mild, such as soreness, redness, tenderness, or swelling where the shot was given.

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) will be closely monitoring for any signs that the 2009 H1N1 vaccine is causing unexpected adverse events, and we will work with state and local health officials to investigate any unusual events.

How will the 2009 H1N1 influenza vaccines be monitored for safety?

CDC and FDA closely monitor the safety of all vaccines licensed for use in the United States in cooperation with stat and local health departments, healthcare providers, manufacturers, and other partners.

The purpose of vaccine safety monitoring is to quickly identify significant adverse events following immunization that may be worrisome enough to consider changing vaccine recommendations. Adverse events, or health problems, following immunization may be coincidental to (meaning occurring around the same time but not related to vaccination) or caused by vaccination. CDC and its partners are using multiple systems to monitor the safety of 2009 H1N1 influenza vaccine. Two of the primary systems are the Vaccine Adverse Event Reporting System (VAERS), which is jointly operated with FDA, and the Vaccine Safety Datalink (VSD) Project.

CDC is also collaborating with partners through the Emerging Infections Program to enhance monitoring of Guillain-Barré syndrome (GBS) during the 2009-10 flu season. For more information on this initiative, see the frequently asked questions on CDC's Vaccine Safety Web page.

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How can adverse events following vaccine administration be reported?

Clinically significant adverse events that follow vaccination should be reported to the Vaccine Adverse Event Reporting System (VAERS), which is a U.S. vaccine safety surveillance system co-managed by CDC and the FDA. Reports can be filled securely online at HHS's VAERS website, by mail, or by fax. Report forms are available online. In addition, report forms or other assistance can be obtained by calling 1-800-822-7967.

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Is the 2009 H1N1 influenza vaccine safest for pregnant women?

Flu vaccines have not been shown to cause harm to pregnant women or their babies. The seasonal flu shot has been recommended for pregnant women for many years. The 2009 H1N1 flu vaccine is being made the same way as the seasonal flu vaccine. Studies that test the 2009 H1N1 flu vaccine in pregnant women began in September. More information is available on this site.

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Can pregnant women receive the nasal spray vaccine?

The nasal spray vaccine is not recommended for use in pregnant women. Pregnant women should not receive nasal spray vaccine for either seasonal flu or 2009 H1N1 flu. After delivery, women can receive the nasal spray vaccine, even if they are breastfeeding. More information is available on this site

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What is thimerosal and does the 2009 H1N1 influenza vaccine contain thimerosal?

Thimerosal is a mercury-based preservative that has been used for decades in the United States and internationally in multi-dose vials (vials containing more that one dose) of some vaccines to prevent the growth of microorganisms, such as bacteria and fungi, which may contaminate them.

The 2009 H1N1 influenza vaccines that FDA licensed are manufactured in several formulations.

Some are produced in multi-dose vials and contain thimerosal as a preservative. Some 2009 H1N1 influenza vaccines are also produced in single-dose units and do not contain thimerosal. In addition, nasal spray is produced in single-dose units and does not contain thimerosal. More information is available on this site

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What is a vaccine adjuvant and will the 2009 H1N1 influenza vaccines that are currently recommended contain adjuvants?

A vaccine adjuvant is a substance that is added to the vaccine to increase the body's immune response to the vaccine.

Vaccine adjuvants will not be used in the United States during the 2009-10 flu season. This includes all of the 2009 H1N1 and seasonal influenza vaccines that will be available for children and adults in both the injectable and nasal spray formulations.

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How will the federal government determine whether people who receive the 2009 H1N1 vaccine have an increased risk for Guillain-Barré syndrome (GBS)?

CDC, FDA, and other federal agencies are tracking GBS through VAERS and several other safety monitoring systems. In VAERS, scientists will assess whether reports of GBS are more common among reports received for H1N1 vaccine compared to seasonal flu vaccine or other vaccines. At the same time, CDC and others are working with neurologists, the medical specialists who see most GBS cases, to encourage reporting of GBS cases through VAERS.

Another system tracking GBS is the Vaccine Safety Datalink project, or VSD. Analysis of VSD information will determine if GBS is more common among people who have received H1N1 vaccine than among people that have not received it. CDC, in collaboration with neurologists, academic centers and state health departments, is also tracking GBS disease among persons in 10 states who are part of CDC's Emerging Infections Program.

If there is an increase in the number of reported cases, public health officials will conduct intensive investigations. If any problems are detected with this 2009 H1N1 vaccine, they will be reported to health officials, healthcare providers, and the public, and health officials will take needed action to ensure the public's health and safety.

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Are there some people who should not receive 2009 H1N1 vaccine?

There are some people who should not get a flu vaccine without first consulting a physician. These include:

• People who have a severe allergy to chicken eggs.
• People who have had a severe reaction to influenza vaccination.
• People who have developed Guillain-Barré syndrome (GBS) within 6 weeks of getting influenza vaccine.
• Children less than 6 months of age (influenza vaccine is not approved for this age group).
• People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated).

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I am allergic to eggs. Can I get the 2009 H1N1 influenza vaccine?

People who have a severe allergy to chicken eggs are among certain groups of people who should not get any flu vaccine (regular seasonal flu vaccine or 2009 H1N1 flu vaccine) without first consulting a physician. This is because both regular seasonal flu vaccine and 2009 H1N1 flu vaccine are made using eggs and each type of vaccine contains tiny amounts of egg protein. Your doctor can best decide if the potential risks of receiving the flu vaccine outweigh the benefits of protection against the flu.

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