By: Col. Lawrence Sellin (Ret.) | CCNS

The following is intended to be an easy-to-understand summary of how the major COVID-19 vaccine candidates work and their current status.

When viruses enter the human body, they attach to specific receptors on the cell surface, enter the cell and then use the cell’s own replicating mechanisms, that is, hijack those mechanisms to replicate themselves and spread the disease.

In response to the viral infection, specifically to the presence of viral proteins, the human immune response is triggered and antibodies are produced to neutralize the virus.

Vaccines work by producing antibodies before exposure to the virus occurs in order to stop an infection from taking hold.

Many vaccines contain live, but “attenuated” viruses, that is, weakened viruses insufficient to cause disease but similar enough to an actual infection to initiate an immune response and the production of antibodies.

Live-attenuated vaccines are used for childhood diseases like measles, mumps, rubella and chickenpox. Because live-attenuated vaccines are so similar to the natural infection they produce a strong and long-lasting, even life-time immune response.

The major COVID-19 vaccine candidate can work in slightly different ways to produce antibodies.

In human cells, the genetic code in Deoxyribonucleic acid (DNA), produces Ribonucleic acid (RNA), which acts as a “messenger” code to manufacture proteins.

Viruses produce proteins in a similar way starting with DNA or, more directly, with RNA. COVID-19 is an RNA virus.

Like viruses themselves, the COVID-19 vaccines make use the protein-manufacturing process in human cells to produce a small, non-infectious piece of the COVID-19 virus, a protein that will initiate an immune response and the production of antibodies that canstop an infection from taking hold.

The Moderna and Pfizer-BioNTech vaccines take a small piece of the COVID-19 RNA, which makes a COVID-19 protein and, when injected in your arm, the muscle cells will make that COVID-19 protein, which is non-infectious in itself, but will trigger an immune response and produce antibodies.

The Oxford-Astra-Zeneca vaccine works somewhat differently to produce the same result, that is, an immune response producing antibodies. Instead of directly after injection into the arm, the small piece of the COVID-19 RNA is carried into human cells by an infectious, but non-replicating virus called adenovirus. That type of vaccine is known as a viral-vector vaccine. Adenoviruses are also used to deliver therapeutics in cancer patients.

So, when the adenoviruses carrying the small piece of the COVID-19 RNA is injected, the adenoviruses will infect human cells, release the small piece of the COVID-19 RNA, which will make the COVID-19 protein. That protein will then trigger an immune response and the production of antibodies like the Moderna and Pfizer vaccines.

The following is what is presently known about the three major vaccine candidates.


  • Efficacy: 95%
  • Vaccine type: mRNA
  • Doses required: 2
  • Storage: Five days in a refrigerator or -70℃ for long-term storage
  • Manufacturing: Up to 50 million doses in 2020 and 1.3 billion in 2021, per Pfizer
  • Cost: $20 per dose
  • State of play: Pfizer has applied for an emergency use authorization (EUA) from the FDA.


  • Efficacy: 94.5%
  • Vaccine type: mRNA
  • Doses required: 2
  • Storage: 30 days in the refrigerator or six months at -20℃
  • Manufacturing: 20 million in 2020 and up to 1 billion in 2021, per Moderna
  • Cost: $32-37
  • State of play: Moderna said it plans to apply for an EUA in the next few weeks


  • Efficacy: 62% to 90%, depending on dosage (average 70.4%)
  • Vaccine type: Combination of common cold virus and coronavirus genetic material
  • Doses required: 1.5
  • Storage: Six months in the refrigerator
  • Manufacturing: Total annual capacity of 3 billion doses, per AstraZeneca
  • Cost: $3-4

The above is intended for informational purposes only and it is always recommended that one consults a physician regarding the prevention and treatment of viral infections.

Lawrence Sellin, Ph.D. is retired from an international career in business and medical research with 29 years of service in the US Army Reserve and a veteran of Afghanistan and Iraq. He is a member of the Citizens Commission on National Security.