Early Results From Clinical Trials Of 2009 H1N1 Influenza Vaccines In Healthy Adults

The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, also is conducting clinical trials of 2009 H1N1 influenza vaccines, produced by Sanofi Pasteur and CSL Limited. The NIAID trials are testing two different dosages (15 micrograms versus 30 micrograms) and evaluating the immune response to one and two doses of these vaccines. More than 2,800 people are participating in ongoing NIAID trials of these vaccines.

Preliminary analyses of early data from the NIAID trials align with the recently announced findings and those to be announced imminently by other companies in that both vaccines studied induced what is likely to be a protective immune response in most adults following a single dose in the same amount (15 micrograms) used in seasonal flu vaccines. Specifically, in blood samples obtained 8 to 10 days after vaccination:

• Among healthy adults who received a single 15-microgram dose of the Sanofi Pasteur vaccine, a robust immune response was measured in 96 percent of adults aged 18 to 64 and in 56 percent of adults aged 65 and older.
• Similarly, among healthy adults who received a single 15-microgram dose of the CSL Limited vaccine, a robust immune response was measured in 80 percent of adults aged 18 to 64 and in 60 percent of adults aged 65 and older.

Additional data from the NIAID trials are forthcoming. However, on the basis of these strong early data, NIAID's results are consonant with other reports that a single 15-microgram dose of unadjuvanted 2009 H1N1 influenza vaccine is well tolerated and induces a robust immune response in healthy adults between the ages of 18 and 64. For adults aged 65 and older, the immune response to 2009 H1N1 influenza vaccine is somewhat less robust, as is the case with seasonal influenza vaccines.

Slight discrepancies seen in the NIAID trials between the Sanofi Pasteur and CSL Limited vaccines may be due to technical differences in the preliminary measurement of the amounts of antigen in the doses used in the clinical trial lots and the relatively limited numbers of samples studied to date, as well as the fact that our data are drawn from a very early time point after immunization.

NIAID will be providing updates on these trials as well as those in children and in pregnant women, which began later.

Information from the NIAID studies will help inform the development of recommendations for immunization schedules, including the optimal dosage and number of doses for different age groups.

NIAID is conducting these clinical trials through its longstanding vaccine clinical trials infrastructure: the Vaccine and Treatment Evaluation Units, a network of medical centers that offers rapid response capability to test vaccines for emerging public health concerns. Detailed information is available from the NIAID Web site (http://www.niaid.nih.gov) and from http://ClinicalTrials.gov.

For more information on influenza, visit http://www.flu.gov for one-stop access to U.S. government information on avian and pandemic influenza. Also, visit NIAID's Flu Portal (http://www3.niaid.nih.gov/topics/Flu/).