What Is in the Flu Shot? Here’s How Experts Explain Common Ingredients

Remember: the ingredients in your flu vaccine are there to keep you safe from a deadly virus.

When discussing the flu shot, it’s important to address prevalent myths and misinformation, with one of the most pervasive and incorrect beliefs being that the flu shot can actually cause the flu.

This misconception stems from a partial truth: the flu shot does indeed contain components of the influenza virus. However, this is done in a way that does not lead to illness. Dr. Tania Elliott, an accomplished infectious disease specialist at NYU, explains that the flu shot is composed of either inactivated virus or viral proteins. These elements serve to stimulate the immune system’s response by prompting the production of antibodies to combat the virus.

In simpler terms, when the body is exposed to the non-infectious virus components, it educates itself to defend against the virus. This preparation equips the body to either prevent illness upon encountering the actual virus or, if infected, to experience a milder form of the illness due to the immune system’s readiness.

Furthermore, it’s essential to clarify that the flu shot is not a static vaccine repeated annually. Rather, it evolves to match the prevailing strains of the flu virus. Each year, an array of flu shot variations is formulated to align with the specific strains of the virus that are anticipated to be prevalent. Dr. Elliot elaborates that a global collaboration of scientists collaborates to identify the most likely circulating strains for the upcoming year. These chosen strains are then incorporated into the flu shot.

The degree of adjustment required varies annually. Some years necessitate minimal alterations, involving only a single strain change. In contrast, other years demand more comprehensive adjustments, entailing modifications to multiple strains. Dr. Sherif Mossad, an expert in infectious diseases at the Cleveland Clinic, emphasizes this dynamic nature of the flu shot, where its composition is tailored to the evolving viral landscape.

OK, but what else is in the flu shot?

The influenza vaccine comprises more than just inactive virus components or fragments. As various flu shots are available annually, there isn’t a standardized ingredient list. However, specific components tend to recur in the composition of different flu shots. If you’re interested in understanding the contents of your chosen flu shot, here are some common components you’re likely to encounter:

Egg protein

You may have come across the notion that individuals with egg allergies are discouraged from receiving flu vaccines. This notion is based on the presence of egg protein in some flu shots.

While it’s accurate that egg protein can be found in numerous flu shots, especially those produced using chicken eggs, having an egg allergy doesn’t necessarily preclude you from getting the flu shot. In fact, the Centers for Disease Control and Prevention (CDC) has explicitly stated that egg allergies should not serve as a barrier to receiving the flu shot. Dr. Waleed Javaid, the Director of Infection Prevention and Control at Mount Sinai Downtown in New York, clarifies that the amount of egg protein contained in the vaccine is extremely minimal, posing no significant risk of triggering an allergic reaction.

However, if you remain uneasy about this matter, it’s worthwhile to have a conversation with your pharmacist regarding the option of receiving an egg-free flu shot.

Preservatives

Certain vaccines incorporate preservatives such as formaldehyde to prevent contamination of the mixtures. Dr. Javaid emphasizes that while encountering substances like formaldehyde in a vaccine might raise concerns about its injection into the body, maintaining a broader perspective is crucial. Specifically, considering the context of the flu shot’s size—0.5 milliliters—is vital. The quantity of formaldehyde present in a flu shot is exceedingly minimal and poses no substantial threat.

It’s worth noting that while formaldehyde can indeed be hazardous if ingested, such as attempting to consume a cup of it, it’s not as unfamiliar to the body as one might assume. In reality, the digestive tract naturally produces formaldehyde. However, for individuals who remain apprehensive, Dr. Javaid reassures that options free of preservatives are available upon request.

Adjuvants

Certain flu shots incorporate adjuvants to enhance the immune response against the influenza virus, essentially bolstering the body’s ability to combat the flu should exposure occur.

In the context of the 2020-2021 flu season, one notable adjuvant utilized in flu shots is MF59. This adjuvant contains squalene, a naturally occurring substance found in both humans and animals. Squalene plays a role in priming the immune system, ensuring it is better equipped to mount a defense against the flu virus.

Another instance of an adjuvant included in some vaccines is aluminum salts, as indicated by the Centers for Disease Control and Prevention (CDC). These adjuvants serve to amplify the vaccine’s effectiveness by enhancing the immune response.

Stabilizers

Stabilizing agents play a pivotal role in the formulation of vaccines by ensuring their efficacy and potency throughout the entire process, from manufacturing to delivery and storage. These agents are integrated into vaccines to counteract factors that could potentially compromise the vaccine’s stability, such as temperature fluctuations and exposure to external contaminants.

During the transportation of vaccines from production facilities to medical centers and pharmacies, a range of environmental conditions can be encountered. Temperature variations and potential disruptions in the cold chain can affect the integrity of the vaccine. Stabilizing agents act as a protective shield, mitigating the impact of these external factors and sustaining the vaccine’s therapeutic properties.

Similarly, once vaccines reach their intended destinations, such as medical facilities or pharmacies, they often need to be stored for extended periods before administration. This storage duration, combined with the need to maintain consistent potency, underscores the importance of stabilizing agents. By preventing deterioration and preserving the vaccine’s composition, stabilizers contribute to the vaccine’s ability to generate an effective immune response.

The CDC acknowledges various stabilizing agents commonly utilized in vaccine formulations. Examples include sugar and gelatin, both of which possess properties that help maintain the vaccine’s structural integrity and prevent the aggregation of vaccine components. These stabilizers not only facilitate safe and efficient vaccine distribution but also ensure that each dose retains its intended immunological effectiveness, ultimately contributing to the vaccine’s successful role in disease prevention.

Antibiotics

When considering the primary purpose of antibiotics – eradicating bacterial infections – the inclusion of antibiotics in the flu shot becomes logical. Dr. Javaid explains that antibiotics are integrated into the flu shot to prevent bacterial growth.

Should you harbor concerns regarding the composition of your flu shot, engaging in discussions with your healthcare provider and pharmacist to determine the most suitable option, such as one free of eggs or preservatives, is highly recommended. Ultimately, experts caution that it’s essential to bear in mind the overarching objective: safeguarding against a potentially fatal virus that claims lives across all age groups. The CDC underscores this urgency, noting that in the 2019-2020 season alone, the virus led to the deaths of up to 62,000 Americans.