With the outbreak of COVID-19, the number of vaccines that have been made around the world is greater than ever before. All these different types of vaccines have the primary goal of providing immunity against the virus and stop it from spreading. However, different vaccine candidates have different ways of working.
Vaccines generally provide immunity by accelerating an immune response to an antigen which is a molecule found on the virus. When it comes to COVID-19 the antigen is generally the standard spike protein found on the body of the virus. The COVID-19 virus generally uses the antigen to infest human cells.
Four Types of COVID Vaccines
As of now, there are four major types of COVID-19 vaccines in clinical trial. Each of these vaccines has a different mode of working. While some of them try to run the antigen into the human body, other vaccine types use the body’s own cells to formulate necessary antigen. The four major types of vaccine candidates are protein subunit, whole Virus, nucleic acid, viral vector.
Protein Subunit type of vaccines utilise pieces of the pathogen which are generally fragments of protein to accelerate the necessary immune response. This decreases the risk of side effects. However, the immune response may be vulnerable. For this reason, to improve the immune response, the vaccine mostly requires adjuvants. The hepatitis B vaccine is an example of Protein Subunit vaccines.
Whole viruses are used by several conventional vaccines to accelerate the immune response. There are two primary ways in which the whole virus triggers an immune response. Firstly, live attenuated vaccines use a weakened form of the virus with the ability to replicate without resulting in illness. Secondly, inactivated vaccines use viruses with destroyed genetic material. This type of virus cannot replicate, but can still trigger an immune response.
Both types of the whole virus use well-established technology and courses for regulatory approval. However, live attenuation may cause disease in people with weak immune systems and often need careful cold storage. Therefore, it is relatively difficult to store whole virus vaccines in low-resource countries.
The third type of vaccine is the nucleic acid vaccines. This type of vaccines use genetic material such as RNA or DNA and informs the cells to create the antigen.
In treating COVID-19, the vaccine type uses viral spike protein and once the genetic material enters human cells, it uses the protein factors from our own cells to create antigen and stimulate necessary immune response. Therefore, this vaccine type can be used on people who have a strong immune reaction as the antigen is produced inside our own cells and in large amounts.
Nucleic Acid vaccines are generally preferred as they are easy to make and cost-effective. However, it has some shortcomings, that is nucleic acid vaccine type has not yet been licensed for human use. Moreover, the nucleic acid vaccine must be kept at ultra-cold temperatures of -70C or lower. This is sometimes challenging for lower-income countries as they may not have specialised cold storage equipment.
The fourth type of vaccine candidate is the viral vector. This vaccine type provides genetic instructions to cells in order to produce antigens. This vaccine type differs from nucleic acid vaccines as they use a harmless virus which is different from the one that the vaccine targets in order to deliver the necessary instructions into the cell.
Similar to nucleic acid vaccines, viral vector hijacks our own cellular machinery to generate antigen from the given instructions, in order to trigger an immune response. Viral vector vaccines can also imitate natural viral infection which makes them capable of triggering a strong immune response. However, since a number of people have already been exposed to the particular viruses being used as vectors, some may be immune to it, which makes the vaccine less effective.