General Information

Flublok (seasonal influenza vaccine) is a trivalent recombinant vaccine for seasonal influenza, made without the use of eggs or the live influenza virus. It contains recombinant HA proteins of the three strains of influenza virus specified by health authorities for inclusion in the annual seasonal vaccine. These proteins function as antigens which induce a humoral immune response, measured by hemagglutinin inhibition antibody.

Flublok is specifically indicted for active immunization against disease caused by influenza virus subtypes A and type B contained in the vaccine, for use in adults 18 through 49 years of age.

Flublok is supplied as a solution for intramuscular injection. Flublok should be administered as a single 0.5-mL dose.

Clinical Results

FDA Approval
The FDA approval of Flublok was based a randomized, double-blind study in 4,648 healthy adult subjects in the US. The subjects received 135 microg of total Flublok (45 microg per strain) or placebo. The primary efficacy endpoint was Centers for Disease Control-defined influenza-like illness (CDC-ILI) with a positive culture for an influenza virus strain antigenically resembling a strain represented in Flublok. CDC-ILI is defined as fever of >100°F oral accompanied by cough, sore throat, or both on the same day or on consecutive days. Attack rates and vaccine efficacy (VE), defined as the relative reduction in the influenza rate for Flublok relative to placebo, were calculated for the total vaccinated cohort. Subjects were followed during the 2007-2008 influenza season. Vaccine efficacy against antigenically matched culture-confirmed CDC-ILI could not be determined reliably because 96% of the influenza isolates obtained from subjects were not antigenically matched to the strains represented in the vaccine. An exploratory analysis of VE of Flublok against all strains regardless of antigenic match isolated from any subject with an ILI, not necessarily CDC-defined ILI, demonstrated an efficacy estimate of 44.8%. HAI antibody responses were seen in 78%, 81%, and 52% of FluBlok recipients to the H1, H3, and B components, respectively. Rates of local and systemic side effects were low, and the rates of systemic side effects were similar in the vaccine and placebo groups.

Mechanism of Action

Flublok is a trivalent recombinant vaccine for seasonal influenza, made without the use of eggs or the live influenza virus. It contains recombinant HA proteins of the three strains of influenza virus specified by health authorities for inclusion in the annual seasonal vaccine. These proteins function as antigens which induce a humoral immune response, measured by hemagglutinin inhibition antibody. The exclusion of eggs and live viris allows Flublok to be made quickly and without any of the infectious risk traditionally associated with vaccine manufacture. Flublok is highly purified, has three times the amount of active ingredient in traditional influenza vaccines, and contains no preservatives (thimerosal), antibiotics or adjuvants.