Vaccine 101

Disclaimer: The views expressed in this blog are meant to provide a summary and overview of the COVID vaccine options. They are not meant to replace official communication, warnings, or guidelines regarding the vaccine. For the most up-to-date information, please refer to the Ministry of Health and Welfare’s Official COVID-19 vaccination website (https://www.mohfw.gov.in/covid_vaccination/vaccination/index.html). You are encouraged to refer to official resources while making and vaccine-related decisions.

No matter where you go, everybody is talking about the COVID-19 vaccines. Should they get the vaccine? If so, which one? To help people make their decision, I will discuss the different types of vaccines out there and whether there is a link between the efficacy and type of vaccine.

What is a vaccine?

The technical definition of a vaccine is a biological agent that elicits an immune response to a specific antigen derived from an infectious disease-causing pathogen (Czochor).

Essentially, a vaccine is a substance that replicates the effect of the actual disease-causing pathogen in your body. The goal is to cause your body to display a response to the vaccine. As a result, if and when you do get the disease in the future, your body would be able to fight it off with ease. It now has a “memory” of how it fought the simulated disease caused by the vaccine. It is imperative that one is vaccinated and is up-to-date with their vaccinations to ensure that they are at low risk of getting the disease for which they could easily be vaccinated.

What are the types of vaccines?

In general, there are six categories of vaccines currently in use.

Type of vaccine	How it works	Examples of its use
Inactivated Vaccine	A dead form of the pathogen is used for inactivated vaccines. These pathogens are grown under controlled conditions and are killed to reduce infectivity and thus prevent infection from the vaccine. Though infectivity is prevented, the structure of the vaccine remains the same, thus eliciting a response from the body’s immune system.	Rabies, Hepatitis A, Cholera, Typhoid, Plague
Live-attenuated vaccines	Live vaccines use a weakened form of the pathogen that causes a disease. Because these vaccines are so similar to the natural infection that they help prevent, they create a strong and long-lasting immune response. Pathogen-specific antibodies are generated. These antibodies are what fight the pathogen if it enters the body in the future.	E.Coli Vaccine, Encephalitis Vaccine
mRNA vaccines	An mRNA vaccine is a type of vaccine that uses a copy of a natural chemical called messenger RNA (mRNA) to produce an immune response in the body. mRNA vaccines manufacture proteins to trigger an immune response. The vaccine introduces molecules of manufactured RNA into immune cells. The RNA that has been placed into the cell functions as mRNA, leading the cell to produce the protein that corresponds to the mRNA code. This protein is normally built by the pathogen itself. The protein stimulates the body’s immune system to destroy the pathogen.	SARS-CoV-2 vaccine
Subunit/polysaccharide vaccines	Also known simply as a subunit vaccine, these vaccines use only a part or unit of the pathogen. It follows a similar principle to the inactivated vaccines. Three possible units could be used. They are the protein, peptide and polysaccharide.	Hepatitis B, Ebolavirus, HIV and Typhoid
Toxoid Vaccines	Toxoid vaccines use a toxin made by the pathogen that causes a disease. It is an inactivated form of the toxin, thus it does not have a direct effect on patients’ health. They create immunity to the parts of the pathogen that cause disease instead of the pathogen itself. That means the immune response is targeted to the toxin instead of the whole pathogen.	Tetanus, Diphtheria
Viral Vector Vaccines	This vaccine type incorporates the use of an organism, such as a virus or bacterium, to transport the gene of the disease-causing pathogen to the human body to stimulate an immunological response. The organism itself is harmless and does not affect the body.	Ebola, SARS-CoV-2 vaccine

Based on the above types of vaccines drug manufacturers have created the following vaccines.

S.No	Name	Vaccine Type	Developers	Efficacy
1	Comirnaty	mRNA-based vaccine	Pfizer, BioNTech; Fosun Pharma	97%
2	Moderna COVID-19 Vaccine	mRNA-based vaccine	Moderna, BARDA, NIAID	94.10%
3	Covishield	Adenovirus vaccine (viral vector)	BARDA, OWS	62%-90%
4	Sputnik V	Recombinant adenovirus vaccine (viral vector)	Gamaleya Research Institute, Acellena Contract Drug Research and Development	92%
5	COVID-19 Vaccine Janssen	Non-replicating viral vector	Janssen Vaccines (Johnson & Johnson)	85%
6	CoronaVac	Inactivated vaccine	Sinovac	50.4%-80.3%
7	BBIBP-CorV	Inactivated vaccine	Beijing Institute of Biological Products	86%
8	Covaxin	Inactivated vaccine	Bharat Biotech, ICMR	81%
9	CoviVac	Inactivated vaccine	Chumakov Federal Scientific Center for Research and Development of Immune and Biological Products	91.40%
10	ZF2001	Recombinant vaccine	Anhui Zhifei Longcom Biopharmaceutical, Institute of Microbiology of the Chinese Academy of Sciences	92%-97%
11	EpiVacCorona	Peptide vaccine	Federal Budgetary Research Institution State Research Center of Virology and Biotechnology	No clear data
12	Convidicea (Ad5-nCoV)	Recombinant adenovirus vaccine (viral vector)	CanSino Biologics	90.7%-95.47%

Relation between type and efficacy?

On average, a vaccine takes several years at minimum to produce, test, manufacture, and administer. But the COVID-19 vaccine has achieved all that within a year while maintaining effectiveness and efficacy. Based on Table 2, we can see that mRNA vaccines have a greater efficacy rate, on average than those produced by a viral vector or an inactivated vaccine method. Now, does the type of vaccine have anything to do with its effectiveness? Or is it that certain drug manufacturers were able to produce a better vaccine than others?

Well, we need to first understand the difference between efficacy and effectiveness. Efficacy can be understood as the percentage reduction of the disease in the vaccinated group of individuals in comparison to those unvaccinated under ideal or controlled conditions. Effectiveness, on the other hand, is the real-world performance of the vaccine.

In an mRNA vaccine, we are targeting a specific protein. As a result, mRNA vaccines would be slightly more effective as the protein being coded by the mRNA in that vaccine is unique to that pathogen. But if the virus mutates, the protein would also change, causing the efficacy to drop. This is observed both in the Moderna and Pfizer vaccines.

When tested with the novel coronavirus, these vaccines have high efficacy, but when tested with the South African strain (B.1.351) or the UK strain (B.1.1.7), their efficacy does experience a drop and the immune response also decreases. However, this is not true for the viral vector vaccines, such as the one being produced by AstraZeneca. Against the novel virus, these vaccines have lower efficacy in comparison to the mRNA vaccines, but when tested against the new strains, it has similar efficacy. This is because viral vector vaccines contain the entire gene of the pathogen rather than just a portion of an RNA that would target a specific protein. A strain is essentially an evolved version of the parental pathogen, so the genetic makeup would be more similar in comparison to the proteins in both pathogens.

That said, this does not mean that one vaccine is better than another. All vaccines have their pros and cons. But what is most important to remember is that when you or anyone you may know has the opportunity to get vaccinated against the coronavirus, you should encourage them to take that opportunity for that is one of the best ways humanity can overcome this pandemic and move on.