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Modern Day Vaccinations and the Race for a COVID-19 Vaccine

Updated: Jul 25, 2021

“As the world is plagued by COVID-19, scientists around the world are scrambling to find a vaccination for this deadly virus. While delving into the chemistry behind how vaccines really work, this article also provides insight into what the future may hold for a possible COVID-19 vaccine.”

Author: Cassandra Lee

In light of the recent COVID-19 pandemic, people around the world have been struggling to come to terms with their ever-changing reality. While most of us have accepted our so-called “new normal”, many are hanging onto the hope of a single word: vaccinations. Since the start of the 20th century, scientists have scrambled to find vaccines for the world’s most notorious pathogens. As a result, diseases such as smallpox, polio, and measles have been quasi eradicated from the developed world [1]. However, the astonishing results of this “miracle” treatment present a simple yet complex question: how do vaccines really work?

Understanding the Issue

Pathogenic substances such as viruses and bacteria are covered in small molecules known as antigens [2]. Upon entering the human body, these substances trigger an immune response through the production of antibodies, which are proteins specifically designed to identify and eliminate pathogenic substances [3]. This concept is implemented in vaccines, which can be defined as “a product that stimulates a person’s immune system to produce immunity to a specific disease…” [4]. Vaccines work by injecting antigens into the body, which allow the immune system to create antibodies to recognize and combat hostile foreigners [2]. Once enough people in a population are vaccinated, herd immunity can be established, in which the number of people immunized renders the possibility of an outbreak very low [2]. The number of individuals that need to be immune in order to establish herd immunity depends on how contagious the pathogen actually is, but the percentage of immunity is usually from 70% to 90% [5]. Eventually, the pathogen will be wiped out when it can no longer spread to new, vaccinated hosts [2]. This allows vulnerable people who cannot be vaccinated, such as pregnant women, young children, the elderly, and those with severe allergic reactions to remain safe from said pathogens [2].

Each individual’s immune system responds differently to pathogens, so various types of vaccines are created to take into account the population that will be immunized, how their bodies will react, and which immunization approach best suits the pathogen in question [6]. Live attenuated vaccines, for instance, introduce a weaker, asymptomatic form of the virus into the body to trigger antibodies without infecting the individual [2]. This form of immunization provides an excellent response due to the presence of real viruses in the body, and has been used to combat diseases such as measles, mumps, influenza and rotavirus [2]. However, live attenuated vaccines, though effective, cannot be given to people with weakened immune systems due to the risk of allowing the pathogen to strengthen and attack the body [2]. On the other hand, inactivated vaccines, which consist of dead pathogens killed through chemicals or heat, can be safely injected into the human body without concerns of a negative response from the virus [2]. Due to its status as a dead pathogen, individuals may need to take several “booster” doses in order to produce a fully immune response [2]. This form of immunization has been used as a treatment for numerous illnesses that were once thought to be incurable such as polio, hepatitis A, and rabies [2].

Subunit or conjugate vaccines, which are used to treat HPV and hepatitis B, are created by isolating a specific protein in the virus, which is then injected into the body to provide immunity [2]. Though both effective and low-risk, this form of vaccination also requires much time and effort to properly extract the correct protein that must be isolated, which is sometimes impossible to determine [2]. Hence, only certain diseases can be treated using this type of immunization.

Other types of vaccines that are currently in development include DNA vaccines, which would consist of injecting a part of the virus’s DNA into the human body, and recombinant vector vaccines, which are created by enveloping a harmless pathogen with a more dangerous virus in order to train the body’s immune response [2].

Figure A [9]

The Race for a Cure

As the race to find a vaccine for COVID-19 rages on, researchers have been looking into live attenuated, inactivated, conjugate, DNA, RNA, and vector vaccines, hoping that one of these trials will hold the key to save the thousands of lives that are at risk due to this virus everyday [7]. In a recent study conducted by CanSino Biologics, a medical company based in China, a recombinant adenovirus type-5 vectored vaccine has been in the works and has already begun human testing and experimentation [8]. This vaccine consists of using a recombinant form of the adenovirus, also known as the common cold [8]. By exchanging a part of the adenovirus gene with SARS-CoV-2, scientists have determined that the modified adenovirus will produce the COVID-19 protein, which will then stimulate an immune response [8]. This vaccine was tested between March 16th, 2020, and March 27th, 2020, where 108 participants, both male and female, were given low, medium, and high doses of the vaccine [8]. Within 7 days, a reaction was seen in 83% of those in the low- and middle-dose groups and 75% of those in the high-dose group [8]. The most common reactions observed were fever, fatigue, headache and muscle pain, and no severe reactions were recorded within 28 days of the trials [8]. Scientists noted that neutralising antibodies increased significantly on day 14, and reached their highest point at 28 days [8]. Similarly, T-cell responses, which are essential to fighting pathogens in the body, peaked 14 days after immunization [8]. The responses seen in these clinical trials suggest that the Ad5 vectored COVID-19 vaccine has potential, and scientists are now investigating this immunization for use in the near future [8].

Looking Forward

With the rapid speed of modern-day research and medical care advancements, vaccinations have proved to be a lifesaving resource to improve the lives of people around the world. Nonetheless, these evolving discoveries are only the tip of the iceberg. As medical professionals continue to break barriers and push the boundaries of contemporary healthcare, it is almost certain that the future of medicine will bring hope of a healthier tomorrow.


Jasmine Kokkat, Winnie Lui, Rhea Verma


Williams Thottungal and Majd Al-Aarg

Additional Credits

Header Image by National Cancer Institute .@nci from Unsplash


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  4. [Internet]. Atlanta (GA): Centers for Disease Control and Prevention; 2020. Immunization: the basics; 2018 May 16 [cited 2020 Aug 16]. Available:

  5. D’Souza G, Dowdy D [Internet]. Baltimore (MD): John Hopkins Bloomberg School of Public Health; 2020. What is herd immunity and how can we achieve it with COVID-19?; 2020 Apr 10 [cited 2020 Aug 23]. Available:

  6. [Internet]. Washington (DC): US Department of Health & Human Services; 2020. Vaccine types; 2020 Mar [cited 2020 Aug 19]. Available:,the%20serious%20diseases%20they%20cause

  7. Chung E [Internet]. Toronto (ON): CBC News; 2020. How close are we to a vaccine for COVID-19?; 2020 Jul 17 [updated 2020 Jul 20; cited 2020 Aug 16]. Available:

  8. Zhu FC, Li YH, Guan XH, Hou LH, Wang WJ, Li JX, et al. Safety, tolerability, and immunogenicity of a recombinant adenovirus type-5 vectored COVID-19 vaccine: a dose-escalation, open-label, non-randomised, first-in-human trial. The Lancet [Internet]. 2020 May 22 [cited 2020 Aug 16];395(10240):1845-1854. Available from: doi:10.1016/S0140-6736(20)31208-3

  9. Schaub N. Antibody explanation [Internet illustration]. 2020 [cited 2020 Aug 16]. Available from:

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