May 17, 2006 (CIDRAP News) – The intranasal influenza vaccine FluMist proved to be 55% more effective than an injectable vaccine in a phase 3 trial of children aged 6 months to about 5 years, according to a press release from MedImmune, maker of FluMist.
The study, involving 8,475 children at 249 sites in 16 countries, was presented May 1 at the annual meeting of the Pediatric Academic Societies in San Francisco.
Lead author Robert B. Belshe, MD, director of the Center for Vaccine Development at St Louis University, said in the press release, "We discovered that [FluMist] was significantly more effective in protecting children against influenza infection. This is especially important, because this age-group is among the most vulnerable to influenza infection, and they tend to spread influenza to other family members."
In the news release, MedImmune cited plans to submit its data to the US Food and Drug Administration (FDA) by the end of June to seek an expansion of FluMist's indications to include children from 6 months to 5 years of age. It is currently approved for healthy children and adults between 5 and 49 years.
In the double-blind study conducted during the 2004-05 flu season, patients received either trivalent injectable inactivated influenza vaccine (TIV) or cold-adapted influenza vaccine, trivalent (CAIV-T). CAIV-T is a refrigerated form of FluMist, designed to be easier to handle than the current version, which must be stored frozen. The study included 6,300 previously unvaccinated children, half of whom were younger than 2 years.
For the strains of influenza that the vaccines were designed for, FluMist was 44% more effective than the injected vaccine (flu attack rates: TIV, 2.4%; CAIV-T, 1.4%). However, FluMist was discovered to be even more effective compared with the injectable vaccine against a variant of the target H3N2 strain that appeared during the flu season studied (attack rates: TIV, 4.5%; CAIV-T, 1.0%), according to MedImmune.
Thus, FluMist had a combined 55% greater rate of effectiveness against both matched and mismatched strains (overall attack rates: TIV, 8.6%; CAIV-T, 3.9%).
William Schaffner, MD, chair of the Department of Preventive Medicine at Vanderbilt University, who was not involved in the study, underscored in a May 1 Associated Press (AP) story the importance of this broader protection. Schaffner said, "That's very, very exciting, because we all know the influenza virus has a tendency to drift," or mutate.
The AP report said that FluMist might work better because it uses live, attenuated virus, as opposed to the dead virus in TIV. Belshe explained in the story that, while injectable vaccine is effective in healthy people who have caught flu before or been inoculated many times, immune-naïve babies and preschoolers need the more flulike nasal challenge provided by FluMist.
MedImmune reported that overall adverse events and serious adverse events were similar in both groups of children, but the FluMist recipients had a 2.5% to 5.6% increase in runny nose and nasal congestion. Also, unvaccinated children experienced a small but statistically significant increase in medically significant wheezing—3.3%, compared with 2.0% in the TIV group.
This increase in wheezing, though, was found only in the 42 days after the first dose, and not beyond 42 days or after the second dose, according to the news release. However, Schaffner, in a USA Today story, said the side effect "will be looked at very critically" by the FDA and by those who make vaccine policy.
May 1 St Louis University press release