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  • Adenoviruses: a common family of viruses. These viruses can cause cold-like symptoms, conjunctivitis (pink eye), sore throat, and other symptoms. The version used in adenovirus vector vaccines is not able to cause these symptoms and cannot replicate. 

  • Adenovirus vector: a version of an adenovirus that cannot replicate or cause disease. They are used in vaccines to deliver genetic information so the body can make a protein that acts as an antigen. 

  • Adjuvant: a compound added to some vaccines to strengthen the immune response

  • Amino Acid: these are the building blocks that make up proteins in the body.

  • Antibiotics: substances that kill bacteria or prevent them from dividing. Antibiotics are used in some vaccines to prevent contamination during the manufacturing process.

  • Antibody: a protein made by the immune system in response to a foreign particle (antigen). These proteins circulate in the blood and help defend the body against the substance.  

  • Antigen: This is any substance that triggers the immune system to create antibodies. For example, allergens such as pollen are antigens. 

  • Asymptomatic: infected but not showing symptoms or signs of disease

  • Attenuated: The pathogen is weakened but not completely inactivated. Attenuated pathogens are too weak to cause disease in almost all people. If you are immunocompromised, talk to your doctor before receiving vaccines containing attenuated pathogens.

  • Bacteria: A type of single-celled organism. Some can cause disease, but many are harmless and some actually benefit humans by living in the intestines and helping with digestion 

  • Bacterium: The singular of bacteria (one bacterium, two bacteria)

  • Buffer: a substance that helps a mixture maintain a specific pH (source)

  • Carbohydrates: another name for sugars

  • Carcinogen: substances that can cause cancer

  • Conjugate: A type of vaccine that attaches an antigen to a protein in order to improve the protection the vaccine provides.

  • Electrolytes: chemical substances with a positive or negative charge that help to maintain the pH and fluid balance in the body so that the organs can function properly. Some common examples of electrolytes are sodium (Na+), potassium (K+), and chloride (Cl-). 

  • Emulsifier: a substance that helps to keep the ingredients mixed together

  • Generally Recognized as Safe (GRAS): A designation from the FDA indicating that an ingredient (usually a food additive) has been shown to be safe based on scientific studies and other uses of the ingredient.

  • Lipid: substances that do not mix with water such as fats, hormones, waxes, and oils

  • Meningitis: inflammation of the lining of the brain and spinal cord

  • mRNA: Messenger ribonucleic acid (mRNA) is a form of genetic material that acts as a template to make proteins. 

  • Nanoparticle: these particles are called nanoparticles due to their size. The dimensions of nanoparticles are in the nanometer range. 1 meter is one billion nanometers.

  • pH: a measure of how acidic or basic a solution is. The scale ranges from 0 (very acidic) to 14 (very basic). A pH of 7 is neutral.

  • Pathogen: a microscopic organism that can cause disease (usually a bacterium or virus)

  • Preservative: a type of ingredient used to prevent contamination

  • Serotype: a group of strains within a species that share a particular type of surface structure. This would be like dividing people into groups based on hair color. Not everyone with brown hair is genetically the same, but members of a species can be put into groups based on a certain shared feature.

  • Strain: Within a particular species there can be a lot of genetic diversity. A strain refers to one member of that species. Similarly, every human is genetically a little bit different but still part of the same species. 

  • Toxoid: an inactive version of a toxin produced by a bacterium. The body is able to make antitoxin without being exposed to the actual toxin. Toxoids are not toxic. 

  • Vaccine Efficacy: How much a vaccine reduces your chance of getting a disease

  • Virus: technically not living organisms because they cannot replicate without a host cell (like a human cell). They are smaller than bacteria.

Units and Conversions:


  • Gram: a unit of mass. A penny weighs 2.5 grams

  • Kilogram (kg): A unit of mass equal to 1000 grams. Also equal to 2.2 pounds.

  • Milligrams (mg): There are 1000mg in 1g

  • Micrograms (µg or mcg): There are 1 million µg in 1g. The symbol µ is the Greek letter mu. 

  • Nanogram (ng): There are 1 billion nanograms in a gram. 

  • Picogram (pg): There are 1 trillion picograms in a gram.



  • Milliliter (mL): There are 1000mL in 1L. 

  • Microliters (µL): There are 1 million µL in 1 liter. The symbol µ is the Greek letter mu.


  • Molarity: It is defined as the moles of a substance in a liter of water. A mole is a standard unit in chemistry defined as 6.022*10^23 molecules of a substance.

  • Parts per million (ppm): A measure of concentration that measures the amount of a particular substance in a larger mixture. 1 ppm would mean that for every 1 million drops of water, there is one drop of the substance you are measuring. It is approximately equal to     1 mg/L of water

  • Parts per billion (ppb): A unit of concentration like ppm, but 1 ppb means that for every 1 billion drops of water there is one drop of the substance you are measuring. It is approximately equal to 1 µg/L of water. 1000 ppb = 1 ppm. 

  • Concentrations can be measured in several ways. These different measurements are useful because substances can have different densities (the same weight can take up different amounts of room based on what it is made of). If you imagine a block of wood and a block of metal that are the same size, they probably do not weigh the same amount because they are different materials and have different densities. 

    • W/W (weight/weight): ​this is a way of defining concentration based on how much the substance weighs compared to how much the total mixture weighs. 1% w/w would be 1 gram of a substance in 100 grams of total mixture. 

    • W/V (weight/volume): this measurement defines concentration based on the weight of the substance compared to the volume of the mixture. 1% w/v would be 1 gram of a substance in 100 mL of total mixture. 

    • V/V (volume/volume): this is a way of defining concentration based on the volume of the substance compared to the total volume of the mixture. 1% v/v would be 1 mL of a substance in 100 mL of total mixture. 

Common Conversions:

  • 2.2 pounds (lbs) = 1 kilogram (kg)

  • 1 kilogram = 1000 grams 

  • 1 gram = 1000 mg = 1,000,000 µg (these conversions are the same for liters)

For more common conversions, click here and here

A Note About Amino Acids:

Enantiomers (mirror images) of alanine

On this website, you may see an amino acid referred to with D- or L- in front of it. D- and L- refer to two different configurations of the same amino acid. 

If you look at your hands, they are mirror images of each other. If both of your hands are face down, they do not fit perfectly on top of each other.

Similarly, D- and L-alanine have the same chemical composition but are mirror images of each other. 


Last updated: Apr. 4, 2024

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