New Data Suggest That a Live Attenuated Influenza Vaccine May Induce Immunity Against Currently Circulating Drifted A/Fujian-Like Influenza Strain

GAITHERSBURG, Md. -- MedImmune, Inc. has announced that it has collected new data from studies with its live, attenuated influenza vaccine showing a strong antibody response against the currently circulating drifted A/Fujian/411/2002 (H3N2)-like strain. These data support results from a pivotal trial for FluMist (Influenza Virus Vaccine Live, Intranasal) that demonstrated the vaccine was safe and 86-percent effective against another drifted A/H3N2 influenza strain in the 1997-1998 flu season (Belshe, Journal of Pediatrics, 2000). The new data come from a preclinical study with FluMist and a clinical trial using an investigational, refrigerator-stable formulation of a live, attenuated flu vaccine (CAIV-T).

"These new data demonstrate that live, attenuated, influenza vaccines may have a greater potential to produce a broad immunity to influenza, including drifted strains, than the inactivated flu vaccines," said Robert B. Belshe, MD, professor of internal medicine and molecular microbiology and immunology at Saint Louis University, and the lead investigator of the pivotal FluMist pediatric trial. "In some years like this one, the strains selected for the flu vaccine will be somewhat different than the strains of flu circulating in the community. While we do not have efficacy data for the specific strains circulating this year, these new data are consistent with earlier studies. This potentially important advantage of a live, attenuated vaccine over inactivated influenza vaccines needs to be further explored in clinical trials."

Each year the U.S. Public Health Service and the World Health Organization (WHO) select the three influenza strains that should be represented in all manufacturers' flu vaccines. The A/H3N2 strain chosen for production of both FluMist and inactivated flu vaccines this season was not optimally matched to the Fujian-like strains currently causing substantial influenza disease.

Data were recently collected from studies in children and animals to determine the ability of the current influenza vaccines to induce immune responses against the drifted A/Fujian-like strain circulating this flu season. In a clinical trial involving 48 children, 67-percent of those immunized with one dose of a live, attenuated influenza vaccine exhibited a significant rise (at least four-fold) in antibody response against the drifted A/Fujian-like strain versus four percent of children who received one dose of an inactivated influenza vaccine. Similarly, in a preclinical study involving ferrets, 88 percent (7 of 8) of the animals receiving one human dose of a live, attenuated flu vaccine had a four-fold rise in antibody response versus zero percent (0 of 8) of the animals receiving one dose of an inactivated vaccine.

To collect additional data on the potential for FluMist to provide an immune response and protection against drifted strains, MedImmune is embarking on a number of studies this flu season, including a recently initiated Phase 4 trial in approximately 250 children receiving either FluMist or the inactivated vaccine. Results from this study are expected by May 2004. In addition, a number of studies are being conducted by leading influenza experts across the country, including Drs. Harry Greenberg and Ann Arvin at the Stanford University School of Medicine; Dr. Arnold Monto at the University of Michigan School of Public Health; Drs. Pedro Piedra and W. Paul Glezen of Baylor University School of Medicine; and Dr. Manju Gaglani of the Scott and White Clinic HMO in Temple, Texas.

FluMist is a live, attenuated influenza vaccine indicated for active immunization for the prevention of disease caused by influenza A and B viruses in healthy children and adolescents, 5 to 17 years of age, and healthy adults, 18 to 49 years of age.

There are risks associated with all vaccines, including FluMist. FluMist does not protect 100 percent of individuals vaccinated. FluMist is not indicated for immunization of individuals less than 5 years of age, or 50 years of age and older. Currently it is unknown whether FluMist will conclusively provide protection against circulating drifted strains.

FluMist is contraindicated in persons with hypersensitivity to any component of the vaccine, including eggs; in children and adolescents receiving aspirin therapy or aspirin-containing therapy; in individuals with a history of Guillain-Barre syndrome; and in individuals with known or suspected immune deficiency. The safety and efficacy of FluMist have not been established in pregnant women or for patients with chronic underlying medical conditions, including asthma or reactive airways disease; the vaccine should not be administered to these patients. In placebo-controlled clinical trials, the most common solicited adverse events in healthy children (n=214) included runny nose/nasal congestion, cough, irritability, headache, decreased activity, sore throat, fever (oral temperature >100 F), muscle aches, chills, and vomiting. The most common adverse events in healthy adults (n=2,548) included runny nose, headache, sore throat, tiredness/weakness, muscle aches, cough, and chills.

Source:MedImmune