Vaccines Do Not Contain: Methylmercury

It is important to understand that there are different forms of mercury. Mercury is a naturally found element in the earth’s crust, air, soil, and water (3). Methylmercury is found in fish, animals, and even humans can be toxic at high levels and lead to adverse effects in humans (1). Such as damage to the nervous system. Which was found to be the case in a case in a population that had prolonged exposure to high levels of methylmercury in their foods. The US has guidelines to try and limit as much methylmercury that is in the environment and food but almost everyone will come be exposed to some degree (2).

(4).

However, there is no methylmercury is vaccines (1,2,3). People sometimes confuse this compound to ethylmercury that is in a compound called thimerosal (2). Ethylmercury is broken down and excreted differently in the body than methylmercury. It is broken down much and excreted much faster. Not only that but Size wise ethylmercury is much bigger and unable to cross the blood brain barrier to cause damage to the nervous like methyl mercury is known for doing (3). Either way, as a precaution in 1999, thimerosal was removed from vaccines to reduce mercury exposure among infants as possible. The only exception was the flu vaccine in multi-dose vials that has thimerosal as a preservative (2).

Resources:

1. American Academy of Pediatrics. (2013, February 28). Vaccine Ingredients: Frequently Asked Questions. Retrieved May 5, 2020, from https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/Vaccine-Ingredients-Frequently-Asked-Questions.aspx
2. Centers for Disease Control and Prevention. (2013, February). Understanding Thimerosal, Mercury, and Vaccine Safety. Retrieved May 5, 2020, from https://www.cdc.gov/vaccines/hcp/patient-ed/conversations/downloads/vacsafe-thimerosal-color-office.pdf
3. Children's Hospital of Philadelphia. (2014, November 5). Thimerosal. Retrieved May 5, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/thimerosal
4. Thimerosal: What to Know About Mercury in Vaccines. (2017, June 05). Retrieved May 07, 2020, from https://www.immunizationinfo.com/thimerosal-what-to-know-about-mercury-in-vaccines/

Vaccines Do Not Contain: Antifreeze

 (4).

There is no antifreeze in vaccines. Antifreeze is typically made with ethylene glycol which is unsafe for humans. People confuse this chemical with polyethylene glycol which is a chemical used in antifreeze but it is also used in many personal care products like skin creams and toothpaste (1).

Although ethylene glycol and polyethylene seem similar they are actually quite different (3). Ethylene glycol can turn into oxalic acid and when this is ingested this causes damage to the heart, kidneys, and central nervous system in large amounts. However, polyethylene glycol is a type of mineral oil and its actually consumed daily as an additive in certain foods and beverages which include soda, ice cream, cookies, and salad dressing (2). Overall, Polyethylene glycol is the chemical in vaccines and it is safe (1).

Resources:

1. American Academy of Pediatrics. (2013, February 28). Vaccine Ingredients: Frequently Asked Questions. Retrieved May 5, 2020, from https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/Vaccine-Ingredients-Frequently-Asked-Questions.aspx
2. Herlihy, S. M., & Hagood, E. A. (2015). Your baby's best shot: Why vaccines are safe and save lives. Lanham, MD: Rowman & Littlefield.
3. Food and Drug Administration. (2019, September 19). CFR - Code of Federal Regulations Title 21. Retrieved May 4, 2020, from

Polysorbate 80

 (2).

It is commonly used in food, cosmetics, and drug formulations as a solubilizer (help make it more soluble), Stabilizer or emulsifier in order to hold the ingredients together that would normally would separate (3, 4). An example, is how water and oil react when mix together. Polysorbate 80 can be found in items such as pickles, vitamins, liquid soap, ice cream in order to keep it from melting, and several vaccines. These uses have been approved by the FDA, and actually the amount in vaccines is very little compared to amount used in vaccines (1).  

Resources:

1. Food and Drug Administration. (2019, September 19). CFR - Code of Federal Regulations Title 21. Retrieved May 4, 2020, from https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=172.840
2. Necessities 101. (n.d.). PURE POLYSORBATE 8020, TWEEN 8020 SURFACTANT EMULSIFIER and EO Fixative. 10oz. Retrieved May 4, 2020, from http://necessities101.com/product/pure-polysorbate-8020-tween-8020-surfactant-emulsifier-and-eo-fixative-10oz/
3. Schwartzberg, L. S., & Navari, R. M. (2018). Safety of Polysorbate 80 in the Oncology Setting. Advances in Therapy, 35(6), 754-767. doi:10.1007/s12325-018-0707-z
4. University of Oxford. (2019, August 30). Vaccine ingredients. Retrieved May 4, 2020, from https://vk.ovg.ox.ac.uk/vk/vaccine-ingredients

Phosphate Buffer

 (2).

These are common are and harmless. They help maintain the pH balance by assuring a substance does not become too alkaline or acidic (3). This reduces the chances the vaccines will have an unwanted reaction and make sure the vaccine works properly (1). Phosphate buffers also keep fragments of active ingredients suspended in the solution so they do not settle. A product called Hank’s Salts, which contains salts based on potassium phosphate and sodium phosphate are used (3). 

Resources:  

1. Herlihy, S. M., & Hagood, E. A. (2015). Your baby's best shot: Why vaccines are safe and save lives. Lanham, MD: Rowman & Littlefield.
2. Fisher Scientific. (n.d.). Aqua Solutions PHOSPHATE BUFFER SOLUTION 1LTR. Retrieved May 5, 2020, from https://www.fishersci.com/shop/products/phosphate-buffer-solution-1ltr/nc9133416
3. University of Oxford. (2019, August 30). Vaccine ingredients. Retrieved May 4, 2020, from https://vk.ovg.ox.ac.uk/vk/vaccine-ingredients

Phenoxythanol, 2-Phenoxyethanol

 (4). 

2-Phenoxyethanol is an organic chemical compound that is sometimes used in cosmetics and antiseptics (1).  It is also currently used as a preservative in one FDA-approved vaccine, called Ipol, for the prevention of polio, at a concentration of 0.5% (3). It is also used as a preservative or stabilizer for other ingredients that might others wise come apart or deteriorate quickly, or become less effective faster (2). The FDA allows the use of this ingredient in cosmetics, and as an indirect food additive and vaccines (3).

It is used in vaccines to kill or prevent the growth of microorganisms in case of an accidental contamination. However, improvements were made in order to decrease the amount used in the vaccines (1).

Resources:

1. Biologics Evaluation and Research, & Food and Drug Administration. (2018, February 1). Thimerosal and Vaccines. Retrieved May 5, 2020, from https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/thimerosal-and-vaccines
2. C. (2018, November 27). Is Phenoxyethanol in Cosmetics Safe? (C. Cobb, Ed.). Retrieved May 5, 2020, from https://www.healthline.com/health/phenoxyethanol
3. Food and Drug Administration. (2019, September 19). CFR - Code of Federal Regulations Title 21. Retrieved May 4, 2020, from
4. Jacobs. (2019, November 15). Parabens Were First-Is Phenoxyethanol Next? Why We Need to Act Now! Retrieved May 5, 2020, from https://www.privatelabelskincareflorida.com/blog/2019/11/15/parabens-were-firstis-phenoxyethanol-next-why-we-need-to-act-now

Weak live virus and Bacteria

 (2). 

Weak live viruses and bacteria or also known as live attenuated are antigens within the vaccines. All vaccines have antigens since these are essential in making them work. They evoke the body to create an immune response in order to form the protection needed for the disease (1). The immune response they invoke is really good since it is close to the response a person would have experienced if they actually had the disease (3).

These weak live pathogens are changed in a lab setting in order they do not cause harm (1). They will grow within someone who is vaccinated but not cause disease but if they do it will be mild (3). However, these pathogens do have a minor change to revert back to their original pathogenic form and cause disease. For this very reason people with compromised immune systems are not able to receive vaccines with these pathogens inside them (3).

Resources:

1. American Academy of Pediatrics. (2013, February 28). Vaccine Ingredients: Frequently Asked Questions. Retrieved May 5, 2020, from https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/Vaccine-Ingredients-Frequently-Asked-Questions.aspx
2. Salerno, A. (2019, September 17). Differences between Live and Dead Vaccines. Retrieved May 5, 2020, from https://www.salernomedical.com/differences-live-dead-vaccines/
3. World Health Organization. (n.d.). Live Attenuated Vaccines (LAV). Retrieved May 5, 2020, from https://vaccine-safety-training.org/live-attenuated-vaccines.html

Sorbitol

 (2). 

Sorbitol is obtained by hydrogenation of D-glucose and it is mainly composed of D-sorbitol. The part that is not D-sorbitol is composed of substances relates to it such as mannitol, iditol, and maltitol (1).

Sorbitol is a type of carbohydrate that is called sugar alcohol or polyol. It has half the sweetness of sucrose (1). It occurs naturally and it is able to produced synthetically from glucose (1). Since sorbitol is found in fruits and berries (4).  It is commonly used as a food additive or sweeteners in foods and drinks (4).  The safety of sorbitol has been reviewed and confirmed by many health authorities around the world. For example, the World Health Organization, the European Union, the U.S. Food and Drug Administration (FDA), and other countries in the world like Australia, Canada, and Japan (3).

Just like any substance moderation is important. Even though it has been shown to be safe since it has been well documented it should still not be had in excessive amounts since it could have potential laxative effects (FOOD). Because when in high quantities the amount of sorbitol that is not absorbed will retain water in the large intestine through osmotic pressure which stimulate peristalsis of the intestine causing it to be a diuretic (1). 

In vaccines sorbitol is used in small quantities as a stabilizer. In a vaccine there could be up to 15 milligrams of sorbitol in the MMR vaccines (VaxPro and Priorix) (4). Sorbitol is overall harmless and has been approved by the FDA to use. However, if someone is allergic to sorbitol or has an intolerance to fructose then they should not receive vaccines that contain sorbitol or be monitored after receiving the injection (4).

Resources:

1. National Library of Medicine, & PubChem. (n.d.). D-Sorbitol. Retrieved May 4, 2020, from https://pubchem.ncbi.nlm.nih.gov/compound/D-Sorbitol
2. PT Sorini Towa Berlian Corporindo. (n.d.). Retrieved May 07, 2020, from http://www.stbc.co.id/product.php
3. Sollid, K. (2019, April 18). What is Sorbitol? Retrieved May 4, 2020, from https://foodinsight.org/what-is-sorbitol/
4. University of Oxford. (2019, August 30). Vaccine ingredients. Retrieved May 4, 2020, from https://vk.ovg.ox.ac.uk/vk/vaccine-ingredients

Neomycin

(1). 

Neomycin is an antibacterial agent (4). Antibiotics are used to prevent bacterial contamination during manufacturing. Most of them are removed during the purification process. Some traces may still remain in some vaccine (2). The reason why most people are trouble by neomycin is because antibiotics are known to cause both local and systemic allergic reactions (2,3). It could be due to hypersensivity to additives found in the in vaccine (3). Since the antibiotics most likely to cause server allergic reactions are not contained in vaccines (2). In fact, neomycin is commonly found in in topical creams, ointments, and lotions (4).

Resources:

1. AED Superstore. (n.d.). FAO Neomycin Antibiotic Ointment 0.9gm, 10 Packs per Box - AED Superstore - A4003. Retrieved May 6, 2020, from https://www.aedsuperstore.com/fao-neomycin-antibiotic-ointment-10-packs.html
2. Children's Hospital of Philadelphia. (2014, November 5). Antibiotics. Retrieved May 6, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/antibiotics
3. Kwittken, P. L. (1993). MMR Vaccine and Neomycin Allergy. Archives of Pediatrics & Adolescent Medicine, 147(2), 128. doi:10.1001/archpedi.1993.02160260018005
4. Ngan, V. (2002). Allergy to neomycin. Retrieved May 07, 2020, from https://dermnetnz.org/topics/allergy-to-neomycin/

Albumin

Egg allergy is one of the more common pediatric food allergies. Typically affecting just 0.5% of the pediatric population (CHOP). Egg allergy even affects 0.2% of adults (1). Someone who is able to eat lightly cooked egg, for example scrambled eggs, without having an allergic reaction is not likely to be allergic. Tolerance does not exclude the possibility of an egg allergy so people who are allergic might be able to tolerate egg in backed products (1). Testing can be done through skin or blood testing for immunoglobulin E against egg protein (2).   

If someone is allergic to egg proteins, called albumin, and get hives after eating eggs in addition to having a history then you are still able get any licensed vaccine that corresponds to their age (1). However, if the allergy is much more severe the person is still able to receive any of the licensed vaccines with egg protein in them, like the flu vaccine (1). However, it is recommended they get the vaccine in inpatient or outpatient medical setting and be under the supervision of a healthcare provider in order to be able manage any severe side effects if they occur (1). 

Resources:

1. Centers for Disease Control and Prevention. (2019, November 25). Flu Vaccine and People with Egg Allergies. Retrieved May 6, 2020, from https://www.cdc.gov/flu/prevent/egg-allergies.htm
2. Children's Hospital of Philadelphia. (2014, November 5). Egg Products. Retrieved May 6, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/egg-products

Thimerosal

Thimerosal is used a preservative in order to prevent the growth of dangerous microbes in case of contamination in mulit-dose vaccines. When each new needle is inserted to the vial. The thimerosal prevents contamination in in the vial when doses are drawn out. This is very important because if someone were to receive an injection that was contaminated it could potentially be very deadly (1).

Thimersosal has been used as a preservative in vaccines since 1940’ (J)s. However, since 1999 thimerosal has only remain in one type of vaccine. Which is the multi-dose Flu vaccine. The FDA decided to this in order to limit the amount of mercury (ethylmercury) children were exposed to, in other words it was a precautionary measure (1).

However, there were concerns in the media about the potential of mercury toxicity from multiple injections in the first few 6 months of life (J). However, people mistook the compound that thimerosal has called ethylmercury from methylmercury. While the two are related they have differences (3).

Methylmercruy is more toxic. It is able to pass the blood brain barrier and damage the nervous system since it is small in size (CHOP). It also has a longer half-life and more lipophilic so the body has a harder time excreting it from the body (3).

On the other hand, ethylmercury has a shorter half-life and the body is able to excrete much faster. It also does not accumulate in the body. Nor does it disease and because of it is bigger in size it is unable to cross the blood brain barrier so it is not able to damage the nervous system (2, 3).   

There were also many reputable studies conducted that have yet to show any link between mercury in vaccine causing autism in children. Different methods have methods have been used and some examined rates of autism in a state or country and compared the rates of autism before and after thimerosal was removed. The results showed that the number of children diagnosed with autism has not gone down since the removal of thiemrosal from vaccines (1). 

Resources:

1. Centers for Disease Control and Prevention. (2013, February). Understanding Thimerosal, Mercury, and Vaccine Safety. Retrieved May 5, 2020, from https://www.cdc.gov/vaccines/hcp/patient-ed/conversations/downloads/vacsafe-thimerosal-color-office.pdf
2. Children's Hospital of Philadelphia. (2014, November 5). Thimerosal. Retrieved May 6, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/thimerosal
3. Clift, K., & Rizzolo, D. (2014). Vaccine myths and misconceptions. Journal of the American Academy of Physician Assistants, 27(8), 21-25. doi:10.1097/01.jaa.0000451873.94189.56

Formaldehyde

There have been concerns about the safety of this ingredient because high concentration of formaldehyde can damage DNA and cause cancerous changes in cells (2). Formaldehyde is a one-carbon aldehyde and highly water soluble. It is used in some vaccines to inactivate viruses and detoxify bacterial toxins as part of the manufacturing process. In the purification process it where steps are taken to remove all formaldehyde in vaccines (4). Sometimes however, some residual formaldehyde may remain but the levels that is left is less or equal to 0.02% (3). This is because in the manufacturing process formaldehyde is diluted (2). The amount of formaldehyde in vaccines is actually several hundred times lower than the amount known to actually cause harm to people, even infants. An example is the DTP-HepB and Hib 5 in 1 vaccine contains less than 0.02% formaldehyde per dose, or less than 200 parts per million (4).

Formaldehyde is even produced naturally in the human body as part of normal metabolic functions to produce energy and build basic materials that are needed for important life process, such as amino acids (2). Human bodies are not able to distinguish between formaldehyde from vaccines or formaldehyde that naturally occur in the body. The amount of formaldehyde in a person’s body actually depend on their body weight. Therefore, even though while babies weigh less than adult they still average a weight of 6-8 pounds and so the amount of formaldehyde in their bodies is 50-70 times higher than the upper amount they are able to receive in a single dose of a vaccine (1).

Resources: 

1. Biologics Evaluation and Research, & Food and Drug Administration. (2018, April 30). Common Ingredients in U.S. Licensed Vaccines. Retrieved April 30, 2020, from https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/common-ingredients-us-licensed-vaccines
2. Children's Hospital of Philadelphia. (2014, November 6). Formaldehyde. Retrieved April 30, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/formaldehyde
3. Mitkus, R. J., Hess, M. A., & Schwartz, S. L. (2013). Pharmacokinetic modeling as an approach to assessing the safety of residual formaldehyde in infant vaccines. Vaccine, 31(25), 2738–2743. doi: 10.1016/j.vaccine.2013.03.071
4. World Health Organization. (n.d.). Components of a Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/vaccine-components.html

Stabilizers

Keeping vaccines stable is very important to keep it working effectively and efficiently. Just like any product as time passes and during temperature changes it decays (1). During cold temperatures it can be unreliable as to what the effects could be. Instability can cause antigens ability to bind specificity. In Live attenuated vaccines it may cause them to be less effective. In bacterial vaccines, they may become unstable due to hydrolysis and the aggregation of protein and carbohydrate molecules (2). Determining the what type of stabilizer to use depends on the vaccine type or more specifically the properties and structure of the active ingredient or viral antigen(s) in the vaccine. Generally, most of the stabilizers found in viral vaccines are considered safe compound (1).  An example of a stabilizer agent is sorbitol (2).  

Resources:

1.  Cardoso, F. M. C., Petrovajová, D., & Horňáková, T. (2017). Viral vaccine stabilizers: status and trends. Acta Virologica, 61(03), 231–239. doi: 10.4149/av_2017_301
2. World Health Organization. (n.d.). Components of a Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/vaccine-components.html

Adjuvants

Adjuvants increase the efficacy of vaccines when they are added because they help induce a better immune response (4). This means they also decrease the number doses required to obtain protective immunity (2). Adjuvants also allow developers to decrease the number of antigens being used, which in some cases can be expensive or in short supply (3).

Vaccines that contain only small components of the pathogen, such protein-based vaccines, rather than the entire pathogen, such as in a live attenuated vaccine, adjuvants are added in order to aid the person in creating a stronger immune response (1). This is beneficial certain population such as people with compromised immune systems, the elderly and the very young because their immune systems may need an extra boost in order to provide the protection they need (3). However, adjuvants may cause local reactions such as redness, swelling, and pain at the injection sit and even more systematic reactions such as fever, chills, and body aches. Even with these minor side effects adjuvants have been used safely in vaccines for many years because they have been tested for safety and effectiveness in clinical trials before being licensed for use in the US and are continuously monitored by CDC and FDA even after approval (1). 

Resources:

1. Center for Disease Control and Prevention. (2018, October 24). Adjuvants help vaccines work better. Retrieved April 29, 2020, from https://www.cdc.gov/vaccinesafety/concerns/adjuvants.html
2. Children's Hospital of Philadelphia. (2014, November 4). About this Section. Retrieved April 29, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients
3. National Institute of Allergy and Infectious Diseases. (2019, July 2). Vaccine Adjuvants. Retrieved April 29, 2020, from https://www.niaid.nih.gov/research/vaccine-adjuvants
4. World Health Organization. (n.d.). Components of a Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/vaccine-components.html

Antigens

These are the active ingredients within a vaccine are that are derived from pathogens and these components are often the whole pathogen, parts of the pathogen, or products made by the pathogen (1). They allow the body to recognize that something is foreign in order to induce an immune response (2). Vaccines may monovalent, meaning they contain a single strain of a single antigen, or polyvalent, meaning they contain two or more strains or serotypes of the same antigen. Within a single vaccine multiple antigens that prevent different diseases can be combined into a single injection, this is useful to overcome difficulties with storing, transporting, and processing. It also helps decrease the number of needle injections a child needs, helping their fear of needles and the pain (3).

Resources:

1. Children's Hospital of Philadelphia. (2014, November 4). About this Section. Retrieved April 29, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients
2. World Health Organization. (n.d.). Components of a Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/vaccine-components.html
3. World Health Organization. (n.d.). Types of Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/types-of-vaccine.html

Antibiotics

Antibiotics are used during the manufacturing process phase to prevent bacterial contamination of the tissue culture cells in which the viruses are grown (2). Most are removed during the vaccine purification process; however, some traces do remain in some vaccines (1). Some parents are worried that some vaccines may be harmful since antibiotics can cause severe allergic reactions in children, such as hives, swelling at the back of the throat, and low blood pressure (2). If people who are allergic to antibiotics need to be closely observed after being vaccinated so that any allergic reaction can be treated as quickly as possible (2). Also, the antibiotics that are most likely to cause severe allergic reactions such as penicillin, cephalosporin, and sulfa drugs are not contained in vaccines. Antibiotics contained in vaccines are polymyxin B, streptomycin, and gentamicin. Even then, the small amounts found in vaccines has yet to be found to cause severe allergic reactions (1).

Resources: 

1. Children's Hospital of Philadelphia. (2014, November 5). Antibiotics. Retrieved April 29, 2020, from https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-ingredients/antibiotics
2.  World Health Organization. (n.d.). Components of a Vaccine. Retrieved April 29, 2020, from https://vaccine-safety-training.org/vaccine-components.html

Herd Immunity and How You Can Help Promote It

Herd immunity is the amount of people within a population that is vaccinated against a disease, which then protects people who are unable to be vaccinated. Depending on the disease there is a certain threshold that needs to be met before herd immunity can work properly. There are certain people who cannot be vaccinated, like very young infants, pregnant women, cancer patients, and, transplant recipients (1).

(2)

Many of the disease that we once faced and being seen less and less, thanks to the use of vaccinations. If we keep vaccinating we can eradicate the diseases that we currently have like we did with smallpox and polio (3). As a human being in this world I do my part by getting my flu vaccine every year, speaking with a travel doctor before leaving the country, and making sure to get boosters when needed. If everyone did that, there would be enough people vaccinated to protect the vulnerable people of our communities. To promote these ideas the blog and other social media sites named the Disgruntled Immunologist was made to help spread the right information about vaccines.

As a scientist and a health care provider it is important to understand that not all parents know science the way we do. They are seeing all of this information from a bunch of different sources, and they do not know who to trust. Speak to the parents as they are equal, stick to the facts, do not over explain things. More often than not people who are vaccine hesitant are trying to do what is best for their child, education and speaking with parents is the best way to do that (4).

¹Coalition , I. A. (2020, April). Science Supports Our Confidence in Vaccines. Retrieved May 2, 2020, from https://www.immunize.org/catg.d/p2073.pdf  

²Helft, L. (2014, September 5). What is Herd Immunity? Retrieved May 2, 2020, from https://www.pbs.org/wgbh/nova/article/herd-immunity/

³Vaccine Glossary of Terms. (2016, May 31). Retrieved May 2, 2020, from https://www.cdc.gov/vaccines/terms/glossary.html#commimmunity 

⁴Vaccines: Vac-Gen/Why Immunize? (2018, July 12). Retrieved May 2, 2020, from https://www.cdc.gov/vaccines/vac-gen/why.htm