High-Dose Influenza Vaccine Shows Increased Immune Response Among Seniors

Sanofi Pasteur, the vaccines division of sanofi-aventis Group, announced today that an investigational high-dose influenza vaccine demonstrated increased immune responses among adults 65 years of age and older compared with the standard influenza vaccine. The candidate high-dose intramuscular formulation of the influenza vaccine is being developed by sanofi pasteur.

The results were reported today at the 48th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC)/Infectious Diseases Society of America (IDSA) 46th annual meeting.

According to the Centers for Disease Control and Prevention (CDC), the currently available inactivated influenza vaccine offers public health benefits in reducing influenza-related morbidity and mortality in older adults. Study authors explain, however, that as people age, the immune system tends to weaken. Older adults become not only more susceptible to infections, but also less responsive to vaccination. When infected with the influenza virus, they are less able to mount an immune response to neutralize the attack.

"Development of an influenza vaccine that will provide an improved immune response in older adults is important because this population has the highest rates of complications from influenza including hospitalization and death," said Ann R. Falsey, MD, associate professor of medicine at the University of Rochester School of Medicine in Rochester, N.Y., and also of the Infectious Diseases Unit at Rochester General Hospital. Approximately 90 percent of the 36,000 average annual influenza-associated respiratory and circulatory related deaths occur among adults 65 years of age and older.

The Phase III study of almost 4,000 people 65 years of age and older compared the high-dose influenza vaccine with the standard inactivated influenza vaccine formulated for the 2006-2007 season. The key finding is that the new high-dose vaccine increased the immune responses to all three influenza strains compared with standard vaccine in the study population. An important additional observation was that the increased immune response was also observed in the potentially more vulnerable subset of study participants who had no measurable circulating protective antibodies before receiving their annual influenza vaccine.

In the randomized double-blind study conducted at 30 centers throughout the United States, 2,575 people received the high-dose influenza vaccine and 1,262 received the standard influenza vaccine. The standard influenza vaccine contained 15µg of hemagglutinin (HA) of each of three influenza strains, and the high-dose vaccine contained four times as much, 60µg HA per strain. Both vaccines contained two influenza type A strains (H1N1 and H3N2) and one influenza type B strain.

After 28 days, investigators assessed serum hemagglutination inhibition (HAI) titers in study participants, a standard measurement of the immune response to influenza vaccination. HAI titers are thought by researchers to correlate with increased protection against illness after exposure to influenza. Statistically significant higher HAI titers against all three influenza virus strains were reported in those who received the high-dose vaccine compared with those who received the standard vaccine. Immunogenicity results met pre-defined criteria for overall superiority of the high-dose vaccine. Pre-defined criteria for overall superiority in the phase III study was based on geometric mean titers (GMT) and seroconversion, which is defined as either a rise in HAI titer from < 1:10 to ≥ 1:40 post-vaccination or a ≥ 4-fold increase in HAI titer post-vaccination from a pre-vaccination titer ≥ 1:10.

In a post hoc analysis, study investigators also examined post-vaccination immune responses induced by the two vaccines among a subgroup of study participants with no protective antibodies (HAI titers less than 1:10 as measured by their pre-vaccination serum sample). This subset of the study population represents a group who may be at even higher risk for severe influenza disease and its associated complications. Among all study participants, 10 percent were seronegative for H1N1, 8 percent were seronegative for H3N2, and 21 percent were seronegative for the B strain. Twenty-eight days after vaccination, a higher percentage of the subgroup given the high-dose vaccine developed seroprotective HAI titers of 1:40 or greater to each of the three vaccine strains compared with those given the standard vaccine. In addition, mean HAI titers for all strains were higher in the seronegative individuals who received the high-dose vaccine compared with those who received the standard vaccine.

Source: sanofi-aventis