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COVID-19 Vaccines Explained

At the close of 2020, two COVID-19 vaccines had received emergency use authorization in the U.S. Experts are optimistic that four others get the OK and reach Americans quickly in 2021. Here's an overview of the authorized U.S. vaccines and the top candidates.

Frontline healthcare workers, nursing home residents and other essential personnel have already received the first dose of either the Moderna or Phizer/BioNTech vaccine. They other vaccines in clinical trials are from Oxford/AstraZeneca, Janssen, Novavax and Sanofi/GlaxoSmithKline (GSK). The UK green-lighted the Oxford/AstraZeneca vaccine Dec. 30.

What do the vaccines do?

Let's start with what they have in common:

  • They are all forms of pharmacogenetics, which is the use of genes in drug technology.
  • They all teach the immune system how to mount a defense against COVID-19.
  • The vaccines carry a piece of the COVID-19 spike protein or instructions on how to make a piece.
  • None of the vaccines infect the body with COVID-19. 
  • Phizer/BioNTech and Moderna vaccines use messenger RNA (mRNA).
  • Oxford/AstraZeneca, Janssen, Novavax and Sanofi/GlaxoSmithKline (GSK) use recombinant DNA (rDNA) and vector virus technology.
  • All of the vaccines are injected into the muscle of the upper arm (intramuscular injections - IM).

What are "pieces of COVID-19 spike protein?

The COVID-19 spike protein is COVID-19's identifying feature. It uses the spike protein to enter cells, and use the cell's functions to make more COVID-19 virus cells. During its replication process the spike protein cleaves, which means it divides into subunits S1 and S2.1 Since the vaccines only introduce a snippet of the spike protein or instructions on how to make a piece of it, the body is not actually infected with COVID-19, according to health experts and the manufacturers.2

How do the Phizer/BioNTech and Moderna vaccines work?

Phizer/BioNTech and Moderna vaccines use nanoparticles to carry mRNA, which are instructions, on how to make a piece of the COVID-19 spike protein. 

How DNA and RNA work: DNA contain instructions for cellular function in the form of code. RNA reads the instructions and transforms in into proteins to carry out the work. mRNA carries the instructions for RNA to decode. With the mRNA vaccines, the body follows the instructions, creates the piece of COVID-19 spike protein, which is then recognized as foreign. The immune system studies it, learns how to destroy it and retains the knowledge.

Phizer/BioNTech and Moderna are the first real world application of mRNA technology in humans. That, along with the speed of their development, has some people afraid or unwilling to take the vaccines. However, according to the US Centers For Disease Control (CDC) clinical trials for mRNA vaccines for influenza, Zika and rabies have been underway for decades and some of the biggest challenges in safety and stability have been mitigated.2

B cells make antibodies, which are Y shaped proteins that attach to pathogens and viruses and disable their ability to infect cells. B cells also retain memory of how to make antibodies for use in case of future attacks. Although antibodies may die, memory B cells and similar memory T cells have been proven in some cases to survive for decades.

See related blog: Boost Your Innate And Adaptive Immunity.

illustration depicting RNA COVID-19 vaccine technology

Two vaccines in use are the first of their kind. All but one of the others next in line use novel technology. The science involves DNA, RNA, nanoparticles and others viruses to enter cells. What does 2021 have in store?

Recombinant DNA/Vector virus Ttchnology

Recombinant DNA technology is the rearrangement of molecules to synthesize genetic material that is entirely new or a replica of something that already exists. Examples of rDNA include vector viruses and the COVID-19 spike proteins used in the COVID-19 vaccines. Other treatments created using recombinant DNA include:

  • Insulin for type 2 diabetes.
  • Sermorelin acetate, also known as GHRH. Sermorelin is a peptide analogue (replica) of growth hormone-releasing hormone. It may be used to diagnose growth hormone deficiency. It may also be prescribed off-label for anti-aging or active aging.
  • Recombinant human growth hormone rhGH indicated to treat growth hormone deficiency.

Vectors are molecular copies of DNA used to carry foreign genetic material into another cell.

The Oxford/AstraZeneca, Janssen and Sanofi/GlaxoSmithKline (GSK) vaccines use modified forms of an adenovirus to deliver the coronavirus spike protein and Novavax uses the influenza virus to transport the spike protein into the cell.

What is an adenovirus?

According to the U.S. Centers for Disease Control and Prevention (CDC), adenoviruses are prevalent and varied. Some are harmless and other cause "gastroenteritis, conjunctivitis, cystitis, and rarely neurological disease." 3 The adenovirus virus used in the vaccine cannot replicate so there is no danger of getting infected by it. However, because humans are exposed to many types of adenoviruses, there is concern that these vaccines may not be as effective as the COVID-19 vaccines because the immune system will destroy the adenoviruses before it can enter cells and deliver the spike protein piece. To mitigate this, adjuvants are used to enhance the effects of the vaccines.

As with the mRNA vaccines, the body studies the COVID-19 spike protein to develop and retain an adaptive immune defense. After it delivers the spike protein, the vector adenovirus and influenza viruses die.

Janssen demonstrates in quick video some of the vaccine's actions once in the body.

Adjuvant Therapies

The Sanofi/GlaxoSmithKline vaccine and the Novavax vaccine use subunit DNA and an adjuvant. The subunits are pieces of the COVID-19 spike protein DNA code that have been singled out as the instructions for the immune system. Adjuvants are pharmacological or immunological agents that improve the effectiveness of the primary drug. Treatments for chronic diseases, cancer, AIDS and autoimmune diseases commonly employ adjuvants. 

How Were The Vaccines Tested?

The clinical trials were multifaceted. In general, participants received either a placebo or the real vaccine. The actions of the vaccine in the body, side effects and participants' resistance to COVID-19 as they went about their life as usual were carefully studied.

Do The Vaccines Prevent COVID-19?

It doesn't look like it. To date during trials, some vaccine participants have been infected with COVID-19 but only mildly. A nurse in San Diego tested positive for COVID-19 six days after getting the Phizer/BioNTech vaccine.

Can I spread COVID-19 if I have been vaccinated?

Probably, given that you can get infected. 

How long does COVID-19 vaccine protection last?

Th CDC website states, "... we won’t know how long immunity lasts until we have a vaccine and more data on how well it works." Antibodies after COVID-19 infection have been detected up to 90 days later. Immunity that develops after an infection is called natural immunity. The duration and robustness of natural immunity depends on the disease and the individual.

Scientists are optimistic that even if antibodies can't be detected after several months, protection may continue in the form of T and B memory cells. 

How effective are the vaccines?

Phizer/BioNTech reports a 95% success rate and the Moderna vaccine according to clinical trials is 94.1% effective. AstraZeneca says its vaccine is 70% effective after one dose. The other candidates haven't released data.

What is the timing of the shots?

All of the vaccines except the Janssen vaccine require two shots. The second shot is called a booster, which is given to prevent the initial immune response from fizzling out.  

The intervals are as follows:

  • Phizer/BioNTech - 21 days
  • Moderna - 28 days
  • The Oxford/AstraZeneca - four to 12 weeks
  • The Sanofi and GlaxoSmithKline (GSK) - interval has not been finalized
  • The NVX-CoV2373 by Novavax - 21 days

Do the vaccines work against the new COVID-19 strain?

The Phizer/BioNTech, Moderna and Oxford/AstraZeneca vaccines were reportedly tested on the variant in the UK and executives announced that their vaccines should be effective. 

What are the side effects?

Side effects reported during the Phizer/BioNTech and Moderna clinical trials included slight and temporary facial paralysis. Since the vaccines have been administered post-trial, there have been a few hundred cases of severe allergic reactions. But all affected have recovered. The National Institute of Allergy and Infectious Diseases is looking into the reactions. The CDC is urging anyone with a history of allergies to injections or any of the ingredients in the vaccines to ask their doctor if it's safe to get the vaccine.4

Can children get vaccinated for COVID-19?

The Pfizer emergency use authorization is for ages 16 and older. Moderna’s is for ages 18 and older, though the company has recently begun testing its vaccine in 12-to 17-year-olds. The other vaccines are being tested in adults 18 and over. Vaccines have not been tested in pregnant women.

What's next?

Several treatments and therapies have already received EU; others are fast underway. Protocol for vaccination priority means that general population may not have access until the spring, according to Dr. Anthony Fauci, National Institutes of Health (NIH) director. Fauci said that the US could return to some degree of normalcy by the fall if 75%-85% of the US population get the vaccine.5

For more information, read COVID-19 Vaccine Choices: Fast Facts.


1. Walls AC, et al. Structure, Function, and Antigenicity of the SARS-CoV-2 Spike Glycoprotein [published correction appears in Cell. 2020 Dec 10;183(6):1735]. Cell. 2020;181(2):281-292.e6. doi:10.1016/j.cell.2020.02.058

2. Understanding and Explaining mRNA COVID-19 Vaccines | Vaccines & Immunizations | Centers for Disease Control and Prevention Accessed January 3, 2021

3. Adenovirus | Clinical Overview | Centers for Disease Control and Prevention Published 2020. Accessed December 31, 2020.

4. COVID-19 and Your Health | Centers for Disease Control and Prevention | COVID-19 Vaccines and Allergic Reactions Published 2020. Accessed December 30, 2020

5. Higgens-Dunn, N., Lovelace Jr., B. Dr. Fauci says U.S. could return to normal by mid-fall if most people get Covid vaccine. Published Dec. 16, 2020. CNBC

Updated Jan. 3, 2021

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