Vaccine Ingredients

Adjuvants are substances added to some vaccines to strengthen the body's immune response to the vaccine antigen. Without an adjuvant, a vaccine might require a higher antigen dose or more doses to achieve the same level of protection. Adjuvants have been used in vaccines since the 1930s.

Aluminum salts are the most widely used adjuvants in vaccines. They have a long safety record and are found in many childhood and adult vaccines including those for hepatitis A, hepatitis B, and diphtheria-tetanus. Other adjuvants include AS04 (used in some HPV and hepatitis B vaccines) and Matrix-M (used in some COVID-19 and influenza vaccines).

Stabilizers protect the vaccine's active components during manufacturing, shipping, and storage. Without stabilizers, the vaccine could lose potency before reaching patients - the active ingredients might break down or become less effective when exposed to temperature changes, humidity, or the physical stress of transportation.

Common stabilizers include sugars such as sucrose and lactose, amino acids such as glycine and glutamate, and gelatin (derived from pork, though pork-free alternatives exist). The specific stabilizer used depends on the vaccine's formulation and storage requirements.

Preservatives prevent bacterial and fungal contamination in vaccine vials, particularly in multi-dose vials where the same container is entered multiple times. Without preservatives, each puncture of the vial septum could introduce contaminants that could cause harm to subsequent recipients.

Thimerosal is the most well-known preservative used in vaccines. It has been used since the 1930s and is still used in some multi-dose influenza vaccine vials. Most single-dose vaccines do not require preservatives because the container is used only once.

Some vaccines use specialized compounds to transport the antigen or help it reach the right part of the immune system. These delivery vehicles serve different functions depending on the vaccine type and platform.

Lipid nanoparticles (LNPs) are used to encapsulate and protect mRNA vaccines, enabling the genetic material to enter cells. Polysorbate 80 is used as an emulsifier in some vaccines to help keep ingredients properly mixed. These compounds became more widely discussed during COVID-19 vaccination programs as public attention on vaccine ingredients increased.

Some vaccines may contain very small amounts of substances left over from the manufacturing process. These are not active ingredients and are not added intentionally - they are trace remnants that remain after purification.

What these are

Tiny fragments or byproducts from the biological systems used to grow or produce vaccine components. For example, viruses used in vaccine production are grown in cell cultures, and the vaccine material must then be separated from the cells.

Why trace amounts may remain

Complete removal of every molecule is not always possible, though manufacturers use extensive purification steps to minimize residual levels. The goal is to reduce these remnants to levels that regulatory agencies have determined to be safe based on the known risk profile of each substance.

Examples

• Residual DNA — tiny fragments from the cells used to grow the vaccine material
• Host cell proteins — small amounts of protein from the cell cultures used in production
• Endotoxins — bacterial byproducts that manufacturers test for and control to very low levels
• Formaldehyde — used to inactivate viruses during production; trace amounts may remain, far below levels that occur naturally in the human body
• Trace antibiotics — used during manufacturing to prevent contamination; antibiotics most likely to cause allergic reactions (like penicillin) are not used in vaccine production

How they are controlled

Regulatory agencies including the FDA and EMA set strict limits on allowable levels of manufacturing residuals in finished vaccines. Each vaccine batch is tested before release to verify that residual levels fall within established safety thresholds.