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October 9, 2009

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Early Results: NIAID Trial Supports Co-Administration of 2009 H1N1 Influenza Vaccine and Seasonal Influenza Vaccine

Early data from a trial evaluating sequential as well as simultaneous administration of the 2009 H1N1 influenza vaccine and the seasonal influenza vaccine in healthy adults indicate that co-administration of the two vaccines does not impair the immune response to either one. The ongoing study is sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

The clinical trial, which began enrolling volunteers on Aug. 7, 2009, has enrolled approximately 400 healthy people aged 18 to 64 years  and 400 healthy people 65 years of age and older. One goal of the study is to determine whether receiving 2009 H1N1 influenza vaccine at the same time as seasonal influenza vaccine has any effect on the body’s ability to produce an immune response predictive of protection against 2009 H1N1 influenza virus. A second goal is to determine if the order of vaccination affects the body’s immune response when the two vaccines are given 21 days apart; data from this part of the trial are not yet available.

In one of the four groups enrolled in this trial, each volunteer received an injection of inactivated seasonal influenza vaccine as well as an injection of inactivated 2009 H1N1 influenza vaccine at the first clinic visit. Study investigators have now analyzed early data from blood samples of some volunteers in this group. Among 25 volunteers aged 18 through 64 years, 76 percent showed a robust immune response to the 2009 H1N1 influenza vaccine. Among 25 volunteers aged 65 years or older, 80 percent developed a robust immune response to the 2009 H1N1 influenza vaccine. These early results support current public health recommendations that endorse simultaneous administration of injectable versions of seasonal influenza and 2009 H1N1 influenza vaccines as one—but not the only—option. The early data from this trial also indicate that both vaccines have been well tolerated.

It is important to note that this trial is analyzing immune responses to injected vaccines containing inactivated influenza virus. Influenza vaccines containing live, attenuated virus delivered in a nasal spray are not being assessed in this trial. The Centers for Diseases Control and Prevention has issued guidance on administering seasonal and 2009 H1N1 influenza vaccines (inactivated or live attenuated) serially or in combination. This guidance is available at H1N1 Clinicians Questions and Answers.

This trial is being conducted at Baylor College of Medicine, Houston; Cincinnati Children’s Hospital Medical Center; The Hope Clinic of Emory University Vaccine Center, Decatur, Ga.; and at St. Louis University, Mo.

Additional information about this trial is available at

Media inquiries can be directed to the NIAID Office of Communications at 301-402-1663,

NIAID conducts and supports research—at NIH, throughout the United States, and worldwide—to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit

NIH...Turning Discovery Into Health ®

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Last Updated October 09, 2009