Author’s note: This blog is part of a series on the current status of the Covid-19 vaccination program in the United States. All information contained herein was obtained from peer reviewed scientific journals and publications as well as legitimate vetted science-based websites. These sources are referenced such that you may obtain further information from them. All information is based on scientific facts known at the time of publication.
How Vaccines Elicit the Immune Response
In the last installment of this series, we saw that vaccine production makes use of various methods such as heat, chemicals, and cell culture to attenuate and weaken microbes that cause disease, in order to use these preparations to inject into the patient to elicit an immune response to the microbe. We will now discuss exactly how this works.
Figure 1 is a schematic representation of the immune response in humans. Humans are exposed to pathogens every day. When a pathogen enters the bloodstream, it is recognized as foreign to the body and B cells attack and phagocytize the pathogen. During this process various antigens of the pathogen are exposed on the surface of the B cells, where they are contacted by and recognized by T cells. This process signals the immune response to the pathogen, whereby memory cells “remember” these protein antigens for future response.
At the same time, an immediate response begins in which plasma cells are made which can produce antibodies against the pathogen. These antibodies are proteins which react to inactivate the pathogen by attaching to and “locking up” the antigens present on the pathogen. This antibody / antigen is very specific; that is the antibodies made in response to a chicken pox virus will not recognize a mumps virus. Every different pathogen elicits a specific antibody response (1).
For diseases that result in debilitation and death, humans can be protected from the disease by being vaccinated. This procedure elicits an immune response to produce antibodies against the pathogen, without the human having to be sickened by the disease. As explained in the last installment, the source of the vaccine must be prepared carefully. In the early years of the oral polio vaccine development, there were instances of the appearance of Vaccine-Associated Paralytic Poliomyelitis cases, due to sometimes incomplete inactivation of the virus particles (2).
Figure 2 is a schematic representation of how the current vaccines being used in the United States to prevent Covid-19 disease are manufactured using the latest technologies. SARS CoV-19 virus particles are treated to release and purify the surface spike proteins, which enable the virus to attach to human cells in order to insert their single stranded RNA genetic information to initiate infection.
The spike proteins are purified and subjected to biotechnology methods which allow for the manufacture of messenger RNA (mRNA) and DNA molecules that will enable a cell to make the spike proteins. Single strand mRNA is very fragile and labile outside of the cell’s protective environment.
The Pfizer and Moderna vaccines utilize a lipid envelope to surround and protect the mRNA strands. This requires that the vaccines be shipped frozen at temperatures below -70 degrees C and -20 degrees C, respectively. The initial studies of the results of vaccination showed that maximum antibody production in patients was obtained by utilizing two shots: an initial injection, followed by a booster approximately 1 month after the initial shot (3). In 1990 the successful use of in vitro transcribed mRNA in animals was reported (4). Since that time additional technological developments and continued research have resulted in mRNA becoming a promising tool in the field of vaccine development (3).
The Johnson and Johnson, and AstraZeneca vaccines use double stranded DNA. However, it is packaged inside a replicant-deficient adenovirus (ChAdOx1) (5). The adenovirus is used as a “delivery vector” for the DNA. Adenovirus vectors were first used in the 1980’s. While they are effective delivery vectors for vaccines, one issue has been the prevalence of variable levels of adenovirus immunity in the human population (6).
Despite the different delivery methods, the idea of using mRNA and DNA as a means to initiate the immune response has come to fruition. In the next installment of this series, we will compare the vaccines that are currently being used for vaccination against Covid-19 disease in the United States.
- Amy E. Thompson, MD. The Immune System. JAMA. 2015;313(16):1686. doi:10.1001/jama.2015.2940
- Anda Baicus. History of polio vaccination. World J Virol. 2012 Aug 12; 1(4): 108–114.
- www.ema.europa/Covid-19 Vaccine AstraZeneca/summary of product characteristics/29 January 2021
- N Pardi, et al. mRNA vaccines — a new era in vaccinology. Nature Reviews Drug Discovery volume 17, pages261–279(2018)
- Lubeck MD, Davis AR, Chengalvala M, et al. Immunogenicity and efficacy testing in chimpanzees of an oral hepatitis B vaccine based on live recombinant adenovirus. Proc Natl Acad SciU S A. 1989;86:6763–7.
- Sai V. Vemula and Suresh K. Mittal. Production of adenovirus vectors and their use as a delivery system for influenza vaccines. Expert Opin Biol Ther. 2010 Oct; 10(10): 1469–1487. doi: 10.1517/14712598.2010.519332
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Clifford M Chapman