After recovering from infectious disease our body gains opposable immunity for invasion of pathogen in the future through ‘Immunological memory’. Immune function can be taught by vaccine without actually getting infected by disease.

Vaccine has to meet two conditions. First of all it should not cause infectious disease from the pathogen. Because the vaccine for the preceding learning of immunity should not be the reason of infection. Second of all the antibody that neutralizes or restrains pathogen must be produced in plasmocyte (=Plasma cell a special cell producing immune antibody as B lymphocyte mutates) and induces the activation of T cells that attack pathogen.

In order to prompt these two conditions the existing vaccines have used the methods which are weakening∙deforming∙inactivating pathogen or using a part of it to serve the similar effect with infection. However thanks to the advancement of biotechnology the vaccine development strategy has been much diversified. Just pieces of antigen are used or like COVID-19 vaccines developed this time mRNA (messenger RNA) or virus-vector that is equivalent to an antigen blueprint are used as vaccines.

Like this case many different vaccines are used depending on the features of disease immunity condition and development convenience nowadays. It is because of the advance of basic science. Especially taking this opportunity that the COVID-19 vaccines become a turning point in human history the development of vaccines overstepping the exist limit can be expected in the future. In this report the type of vaccines and COVID-19 vaccines that currently commercialized or are undergoing the clinical trials will be introduced.

The component of live attenuated influenza vaccine (LAIV) is a living pathogenic organism that is deformed or diminished its pathogenicity. The deformed pathogens provoke limited infection and light symptoms or do not cause any disease when it is injected to human body. It is used for bacteria vaccines rather than virus vaccines. Because the mechanism is similar to natural infection it is strong and lead immune reactions that last longer. LAIV method is used for measles mumps rubella rotavirus smallpox chickenpox and yellow fever. There is no LAIV currently developing for COVID-19.

Inactivated vaccine uses the pathogens inactivated (or killed) by chemical substances such as heat radiation or formaldehyde to make its proliferation inoperable. Therefore it does not cause diseases or activate even if the vaccines are injected. Unlike LAIV it has a higher stability since it does not use living pathogens but relatively it has short lasting period and low immune reactions. Because of this reason it is vaccinated multiple times in order to increase its efficiency and make it last longer. Inactivated vaccines are used for the diseases such as hepatitis A influenza infantile paralysis and rabies.

The COVID-19 vaccines that are being developed by Sinopharm Wuhan Sinopharm Beijing and Sinovac the state-owned Chinese pharmaceutical companies are equivalent to inactivated vaccines and currently undergoing the phase 3 clinical trial. It is narrowly vaccinated in China. There is a claim that it shown 78% of preventive effect in phase 3 clinical trial targeting about 12000 people in Brazil. However scientific evidence has not been revealed so it is too early to judge its effect. Furthermore there are some reports saying India has shown high preventive effect with the independent development and vaccination but the statistics and proof are still uncertain.

If both of LAIV and inactivated vaccines are using the whole pathogens subunit protein vaccine uses the specific protein pieces (Peptide) that consists of shields of pathogens and cell membrane or polysaccharide as a chief component. The protein used in this case is refined and mass-produced by using genetic recombination technology. Subunit protein vaccine has few side effects and is safe but it shows low immune reactions so it is injected with an immune booster (Adjuvant) to elicit a higher immune reaction. It is used for influenza pertussis and malaria vaccines.

The COVID-19 vaccines which is being developed by domestic company SK bioscience and currently undergoing the phase 1 clinical trial is a subunit protein vaccine. SK bioscience has developed the vaccines by using the spike protein from the surface of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2) as antigen. In overseas the vaccine from Novavax in the US ‘NVX-CoV2373’ is a subunit protein vaccine. It is currently implementing the phase 3 clinical trial so it is leading ahead. NVX-CoV2373 has a great benefit that it is covered with saponin which is from plants so it can be kept off allergic reactions.

Virus-like particle is a particle that only consists of the shield of outer protein with no genetic code. Some virus protein assembles and forms virus-like particle which is a similar structure with the original virus however they do not have any viral genetic material so infection or proliferation is impossible. Best-known virus-like particle vaccine is cervical cancer vaccines (Cervarix and Gardasil) targeting Human Papilloma Virus (HPV).