BETHESDA, MD 17 January 2013—FDA on Wednesday approved the licensing of Flublok, the nation's first trivalent seasonal influenza vaccine that contains recombinant viral proteins instead of antigens derived from live virus.
Limited amounts of Flublok will be available during the current flu season, according to Meriden, Connecticut-based Protein Sciences Corporation.
Flublok is indicated for use in adults 18–49 years of age and is administered as a single, 0.5-mL dose, according to the product's labeling (PDF).
Each dose of the vaccine contains 45 μg of purified recombinant hemagglutinin corresponding to the hemagglutinin antigens from each of the influenza virus strains selected for the flu season's trivalent vaccines.
The proteins in Flublok are derived from a recombinant baculovirus vector and expressed in a continuous insect cell line.
The vaccine will be supplied in cartons of 10 single-dose vials for intramuscular injection. The vials should be refrigerated and protected from light. If freezing occurs, the vaccine should be discarded.
According to FDA, Flublok must be used within 16 weeks after its production. The agency urged health care providers to carefully check the expiration date before administering the vaccine.
In clinical trials, the most commonly reported adverse events associated with Flublok were injection-site reactions.
Flublok is the second FDA-approved cell-based vaccine for protection against seasonal influenza. Flucelvax, by Novartis Vaccines, was licensed in November. Flucelvax is derived from live virus grown in a canine cell line and is not a recombinant vaccine.
Efficacy data for Flublok came from a placebo-controlled clinical trial involving 4648 patients that was conducted during the 2007–08 flu season.
Flublok's overall efficacy during the study was 44% against all strains of circulating viruses.
According to the labeling, the efficacy of Flublok against the three strains used in the vaccine could not be determined because 96% of the viruses isolated during the study did not match the vaccine strains.
The Centers for Disease Control and Prevention (CDC) reports that during the 2007–08 flu season, 66% of influenza type A H1N1 viruses characterized by the agency matched the vaccine strain, as did 23% of influenza type A H3N2 viruses and 2% of influenza type B viruses.
CDC's initial estimates from the current flu season indicate that the available vaccines are about 60% effective for the prevention of influenza.