What are the ingredients in the COVID-19 (Coronavirus Disease 2019) vaccine?

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Last updated: October 22, 2025 • View editorial policy

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COVID-19 Vaccine Ingredients

The main ingredients in COVID-19 vaccines include mRNA or viral vectors (active components), lipid nanoparticles (delivery systems), polyethylene glycol (PEG), polysorbate, and various stabilizers, with specific formulations varying by manufacturer. 1

mRNA Vaccine Ingredients (Pfizer-BioNTech and Moderna)

Active Components

  • mRNA encoding the SARS-CoV-2 spike protein - the primary immunogenic component that teaches cells to produce the viral protein, triggering immune response 1
  • Nucleoside-modified mRNA (modRNA) is used to enhance stability and reduce inflammatory responses 1

Delivery System

  • Lipid nanoparticles (LNPs) - essential for protecting the mRNA and facilitating cellular uptake 1
  • Components of LNPs in Pfizer/BioNTech vaccine include:
    • ALC-0315 (ionizable lipid) - novel component that helps mRNA enter cells 1
    • ALC-0159 (polyethylene glycol [PEG]-phospholipid conjugate) - stabilizes the formulation 1
    • Cholesterol - complies with European Pharmacopoeia and is used in several approved products 1
    • Distearoyl phosphatidylcholine (DSPC) - structural lipid component already used in other approved products 1

Excipients and Stabilizers

  • Polyethylene glycol (PEG) - enhances stability of the mRNA-containing lipid nanoparticles 1
  • Salts (potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate) - maintain pH balance 1
  • Sucrose - acts as a cryoprotectant to protect the vaccine during freezing 1

Adenoviral Vector Vaccine Ingredients (AstraZeneca and Johnson & Johnson)

Active Components

  • Replication-deficient adenovirus vector encoding the SARS-CoV-2 spike protein 1
  • Oxford/AstraZeneca uses chimpanzee adenovirus (ChAdOx1) 1
  • Johnson & Johnson uses human adenovirus type 26 (Ad26) 1

Excipients

  • Polysorbate 80 - used as a stabilizer in adenoviral vector vaccines instead of PEG 1
  • Various salts and buffers to maintain pH and stability 1

Potential Allergens and Safety Considerations

  • PEG and polysorbate are the primary components associated with allergic reactions 1
  • Allergic reactions to COVID-19 vaccines are rare but can occur through:
    • IgE-mediated pathways - triggered primarily by non-active ingredients like PEG 1
    • IgE-independent pathways - involving complement system activation 1
  • CDC data showed approximately 11.1 cases of anaphylaxis per million doses of Pfizer/BioNTech vaccine during initial rollout 1
  • Individuals with history of severe allergic reactions to injectable medications, vaccines, or PEG/polysorbate-containing agents should be evaluated carefully 1

Important Considerations for Special Populations

  • The ingredients in COVID-19 vaccines do not contain egg protein, gelatin, latex, or preservatives like thimerosal 1
  • Both mRNA and adenoviral vector vaccines are non-live vaccines, making them suitable for immunocompromised patients 1
  • The 2024-2025 COVID-19 vaccines have been updated to target currently circulating strains (Omicron JN.1 lineage and KP.2) 1
  • Moderna and Pfizer-BioNTech use the KP.2 strain, while Novavax uses the JN.1 strain in their 2024-2025 formulations 1

Clinical Implications

  • Detailed allergy history should be taken before vaccination, particularly focusing on previous reactions to PEG or polysorbate-containing products 1
  • For patients with history of allergic reactions, skin testing for PEG and polysorbate may be considered before vaccination 1
  • In cases of positive skin tests to these components, vaccination may be contraindicated under Emergency Use Authorization 1
  • Measuring serum tryptase and complement system elements may help diagnose vaccine-induced reactions following COVID-19 vaccination 1

The COVID-19 vaccines have demonstrated favorable safety profiles overall, with the benefits of vaccination significantly outweighing the risks of rare adverse events, particularly in terms of preventing severe disease and death from COVID-19 infection 1.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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