The term “flu shot” is the common, informal name for the annual preventative measure against seasonal influenza viruses. This vaccination is a public health measure intended to reduce the risk of infection and severe illness caused by the flu. The product is properly known as the influenza vaccine, and its specific formulation is adjusted each year to match the influenza strains predicted to be circulating.
The Influenza Vaccine: Generic Names and Designations
The generic name for the injection is the Inactivated Influenza Vaccine (IIV), as it contains non-infectious, killed virus components. Vaccines are classified by the number of viral strains they protect against. For several years, the standard type was the quadrivalent vaccine, which contained components for four different strains: two Influenza A strains (H1N1 and H3N2) and two Influenza B strains.
The composition is reviewed annually by organizations like the World Health Organization and the Centers for Disease Control and Prevention. Due to the B/Yamagata virus lineage not being detected since early 2020, many regions are transitioning back to a trivalent vaccine formulation. The trivalent vaccine protects against three strains: the two Influenza A strains and only one Influenza B strain (B/Victoria lineage).
Delivery Methods: Injection Versus Nasal Spray
The most common delivery method is the standard intramuscular injection, usually given in the upper arm. This traditional “flu shot” is an inactivated vaccine, meaning the viruses it contains have been chemically treated to prevent infection. This type is widely approved for most individuals six months of age and older and has a long-standing safety profile.
A notable alternative is the nasal spray vaccine, properly called the Live Attenuated Influenza Vaccine (LAIV). The LAIV contains weakened, live flu viruses that are cold-adapted to replicate only in the nasal passages, not in the lungs. This method is typically approved for non-pregnant individuals between the ages of two and 49 years. Because it contains a live virus, it is not recommended for certain groups, such as those who are immunocompromised or have specific underlying medical conditions.
Specialized Options for Specific Populations
Specialized formulations are designed to enhance protection for particular demographic groups.
High-Dose Vaccine
One option is the high-dose vaccine, licensed specifically for adults aged 65 years and older. This product contains four times the amount of antigen compared to a standard-dose shot. The increased antigen load is intended to elicit a stronger immune response in older adults whose immune systems naturally weaken with age.
Adjuvanted Vaccine
Another specialized vaccine for the 65-and-older population is the adjuvanted vaccine. This formulation includes an adjuvant, an ingredient added to enhance the body’s immune response to the vaccine. The adjuvant boosts the protection provided by the vaccine, making it more effective for individuals who may have a diminished response to standard vaccines.
Egg-Free Vaccines
A third category includes the egg-free vaccines, beneficial for people with severe egg allergies or those seeking alternatives to traditional production methods. These are manufactured using cell-based technology, where the virus is grown in animal cells instead of chicken eggs, or through recombinant technology. Recombinant vaccines are manufactured by inserting a specific gene into a virus to produce a key flu protein, which is then purified and used in the vaccine.