The FDA approval letter describes Flublok as follows:

"It is an influenza vaccine formulated as a sterile, aqueous, buffered solution of purified, recombinant influenza hemagglutinins (rHAs) and contains no egg proteins. The three rHAs are produced in Spodoptera frugiperda insect cells using a Baculovirus Expression Vector System (BEVS) in which the insect cells are infected with a baculovirus engineered to contain the gene for the corresponding influenza HA antigen. Each 0.5 mL dose of Flublok contains 135 mcg of rHA antigens (45 mcg each of H1, H3 and B rHAs) and may contain residual amounts (≤28.5 mcg) of baculovirus and insect cell proteins."

The approval letter also states that Flublok was originally approved for persons 18-19 years of age on January 16, 2013. The approval letter below is for persons 50 years of age and older.

 Summary Basis for Regulatory Action (FDA)

In order to better understand the science behind the new vaccine (compared to egg-based vaccines that were developed before 1940), an illustration of BEVS, mentioned above, is provided here (copied from one of the manufacturer's public presentation):

Press release of the Jan 16, 2013 approval:

FDA approves new seasonal influenza vaccine made using novel technology

Press release dated June 3, 2015 by Protein Sciences Corporation regarding 12 year exclusivity granted by FDA:

FDA Grants 12 Year Exclusivity to Flublok Influenza Vaccine