Several different types of influenza vaccines are available each season, going far beyond a single, standard shot. A “flu shot” is a broad term for a vaccine designed to protect against the specific influenza strains predicted to circulate. These vaccines vary in composition, manufacturing method, and the specific populations they are intended to protect.
Standard Seasonal Vaccinations
The most widely administered influenza vaccine is the standard-dose shot, which is approved for the general population, including children as young as six months old up to adults aged 64. This vaccine is typically quadrivalent, meaning it is formulated to protect against four different influenza strains: two influenza A viruses and two influenza B viruses. The inclusion of four components provides broader protection against the variety of viruses that may be circulating during a flu season.
Standard inactivated influenza vaccines are produced using two primary methods. The long-standing egg-based method involves growing the flu virus in fertilized chicken eggs before inactivation and purification. Alternatively, the cell-based method grows the virus in cultured mammalian cells, avoiding the use of eggs entirely. Both manufacturing platforms yield a vaccine with comparable protection for the average healthy individual.
Enhanced Options for Specific Populations
Specialized enhanced vaccines are available to boost the immune response in individuals whose immune systems may not respond robustly, particularly adults aged 65 and older. These options are preferentially recommended for seniors due to their increased risk of severe illness, hospitalization, and death from influenza. They aim to overcome the natural decline in immune function that occurs with age.
High-Dose Vaccine
The high-dose vaccine contains four times the amount of the hemagglutinin antigen compared to a standard dose. Delivering a larger quantity of this surface protein encourages the immune system to produce a stronger and more protective antibody response.
Adjuvanted Vaccine
The adjuvanted vaccine contains the same amount of antigen as a standard dose but includes an ingredient called an adjuvant. This adjuvant acts as an immune-system stimulant, creating a more vigorous and prolonged reaction to the vaccine.
Alternative Delivery and Composition
Beyond the traditional injected shots, alternatives exist that differ in their method of administration or their composition. One such alternative is the live attenuated influenza vaccine (LAIV), commonly administered as a nasal spray. This vaccine uses weakened, live viruses that stimulate an immune response primarily in the mucosal lining of the nose and upper airways.
The nasal spray is a needle-free option approved for healthy, non-pregnant individuals between the ages of 2 and 49, but it is not recommended for those with certain chronic medical conditions. Another distinction involves egg-free production, specifically the recombinant vaccine. The recombinant vaccine is created synthetically by inserting genetic information for the flu virus’s surface protein into cultured cells, bypassing the use of chicken eggs entirely. This makes it a suitable choice for individuals with severe egg allergies.