Influenza vaccine development has moved beyond the century-old method of using fertilized chicken eggs. Modern technology has introduced a new generation of vaccines using advanced manufacturing platforms. Among these are Flublok, a quadrivalent recombinant influenza vaccine, and Flucelvax, a quadrivalent cell culture-based inactivated influenza vaccine. Both aim to improve production speed and ensure a closer match to circulating virus strains. Understanding how these vaccines are created and stimulate the immune system clarifies their roles in seasonal flu prevention.
Understanding How They Are Made
The core distinction between Flublok and Flucelvax lies in their distinct methods of antigen creation. Flublok is manufactured using recombinant DNA technology, bypassing the need for the influenza virus or animal products like eggs. This process starts by identifying the genetic sequence for the hemagglutinin (HA) protein, the surface protein that triggers the immune response. Scientists combine the HA gene with a baculovirus, which infects cultured insect cells derived from the fall armyworm. These cells rapidly produce large quantities of the purified HA protein. The final vaccine contains only this purified protein antigen, not an inactivated virus, making it an entirely synthetic product matched to the targeted strain sequence.
Flucelvax utilizes a cell culture-based method, substituting mammalian cells for chicken eggs. The vaccine virus strains are grown in cultured Madin Darby Canine Kidney (MDCK) cells. Once the viruses replicate, they are harvested, purified, and chemically inactivated to create the final vaccine. This cell-based approach avoids egg-adaptation. When a virus is grown in eggs, it can mutate, resulting in a vaccine antigen slightly different from the wild-type virus circulating in the human population. By using a mammalian cell line, Flucelvax aims to produce a truer antigenic match to the strains selected for the season.
Performance and Immune Response
The unique manufacturing processes translate into different strategies for generating protection. Flublok is formulated with a higher concentration of the active ingredient, containing three times the amount of hemagglutinin antigen compared to a standard-dose shot. This high-dose approach is designed to produce a more robust immune response, which can be advantageous for certain populations. Clinical studies suggest this increased antigen content results in higher levels of protective antibodies. The recombinant technology also induces a broader immune response, helping guard against strains that have slightly “drifted” or mutated away from the vaccine’s target. This enhanced immune breadth is a benefit when circulating virus strains are not perfectly matched.
Flucelvax’s performance advantage stems from its ability to produce an antigen that is a closer genetic match to circulating influenza strains. Since the cell-based method avoids egg-adaptation mutations, the resulting vaccine component is more likely to resemble the actual virus targeted for the season. This precision in matching improves vaccine effectiveness, especially in seasons where egg-adaptation is an issue. Observational studies sometimes indicate that cell-based vaccines provide greater protection against flu-related illness compared to standard egg-based vaccines. Both Flublok and Flucelvax overcome limitations of older production methods, either through high-precision engineering and a higher dose, or through maintaining the fidelity of the viral antigen.
Recommended Usage and Administration
Age approval is a clear difference between the two vaccines. Flucelvax has the broader indication, approved for individuals beginning at six months of age, making it an option for nearly anyone eligible for a flu vaccine. In contrast, Flublok is currently approved only for adults aged 18 years and older. Although the high-dose formulation is often discussed for older adults with weaker immune responses, it is approved for all adults in this age range. Both vaccines are administered as a single, intramuscular injection, similar to a standard flu shot.
The question of egg allergy is relevant, though less concerning than in the past. Both Flublok and Flucelvax are considered egg-free because they do not rely on fertilized chicken eggs. Flublok is egg-protein free due to its synthetic recombinant process, and Flucelvax is manufactured entirely in mammalian cell culture. Current recommendations state that individuals with an egg allergy may receive any age-appropriate influenza vaccine. However, Flublok and Flucelvax remain important non-egg-based alternatives. The final choice often depends on a patient’s age, local availability, and a healthcare provider’s assessment of which vaccine profile best suits the patient’s needs.