Cold Adapted Influenza Vaccine (Liquid Formulation) CAIV-T
CAIV-T is an investigational intranasal, cold-adapted trivalent influenza vaccine. It is the refrigerator-stable formulation of FluMist®, which is a frozen, live attenuated cold-adapted trivalent influenza vaccine. To date, the safety, tolerability and efficacy of CAIV-T has been studied in both healthy and at-risk populations between the ages of 6 weeks and 98 years.
On May 1, 2006 at the Pediatric Academic Societies' annual meeting, MedImmune presented its pivotal Phase 3 study for CAIV-T, entitled, "Comparison of the Efficacy and Safety of Cold-Adapted Influenza Vaccine, Trivalent With Trivalent Inactivated Influenza Vaccine in Young Children 6 to 59 Months of Age." The study included 8,475 children at 249 sites in 16 countries in North America, Europe, the Middle East and Asia. Study participants were randomized one-to-one to receive either CAIV-T or the flu shot during the 2004-2005 influenza season. Each participant also received a placebo nasal spray or placebo injection to preserve the double-blind design of the study. Participants were followed through the influenza season and evaluated to identify illnesses caused by influenza virus. The trial included more than 6,300 previously unvaccinated children and nearly 50 percent of the children enrolled were less than 2 years of age.
The results of this trial showed that CAIV-T was 55 percent more effective than the trivalent injectable inactivated influenza vaccine (TIV) in reducing influenza illness caused by any influenza strain in children 6 months to 59 months of age, including both matched and mismatched strains. The influenza attack rate was 8.6 percent for study participants receiving the flu shot compared to 3.9 percent for those who received CAIV-T (P <0.001). Against matched strains alone, CAIV-T was 45 percent more effective than the flu shot (attack rates: TIV = 2.4 percent, CAIV-T = 1.4 percent; P<0.001). In this study, CAIV-T also appeared to be 89 percent more effective than the flu shot in reducing influenza illness caused by the matched H1N1 A strain (attack rates: TIV = 0.7 percent, CAIV-T = 0.1 percent; P<0.001) and 79 percent more effective than the flu shot against the circulating mismatched H3N2 A strain (attack rates: TIV = 4.5 percent, CAIV-T = 0.9 percent; P<0.001). There were no cultures of mismatched H1N1 strains or matched H3N2 strains detected in the trial. While there were 16-percent fewer children with illnesses associated with B strains in the CAIV-T group compared to TIV (attack rates: TIV= 3.5 percent, CAIV-T = 2.9 percent), this difference was not statistically significant.
In the study, the overall incidence of adverse events and serious adverse events was similar in both groups except for a higher incidence of runny nose and nasal congestion in CAIV-T recipients (4.4 ~ 11.1 percent increase) and a higher incidence of injection site reactions in those receiving the flu shot (3.6 ~ 7.6 percent increase). A statistically significant increase in the incidence of medically significant wheezing was seen in CAIV-T recipients 6 months to 23 months of age within 42 days following vaccination. Post-hoc analyses showed higher all-cause hospitalizations occurring through 180 days after vaccination in CAIV-T recipients 6 months to 11 months of age. Risk- benefit analyses showed a favorable profile for CAIV-T as compared to TIV in children 12 months to 59 months of age without a prior history of wheezing or asthma.