COVID-19 Vaccines Differing in Mechanism and Characteristics


Vaccines from AstraZeneca and Janssen exhibiting thermal stability
mRNA vaccines from Pfizer and Moderna manufactured on a large scale

With the forthcoming introduction of vaccines for the novel coronavirus (COVID-19) in Korea, the characteristics of each vaccine are drawing attention.

COVID-19 vaccines are being developed at record speed worldwide, with the use of diverse vaccine platforms. A “vaccine platform” refers to the underlying vaccine technology that is used to develop a specific vaccine by simply changing the antigen or genetic information. Vaccine platforms include viral vector vaccines, RNA vaccines, recombinant vaccines, and inactivated vaccines.

On January 7, the Ministry of Food and Drug Safety (MFDS) released a reference material that presents information on the characteristics and mechanisms of different COVID-19 vaccines that are available.

Thermally stable viral vector vaccines developed by AstraZeneca and Janssen

A viral vector vaccine is created by inserting the antigen gene into a viral vector that is harmless to the human body, such as adenoviruses, and administered to induce an immune response through the synthesis of antigen proteins in the body.

Examples of COVID-19 vaccines in the form of a viral vector vaccine are the ones from AstraZeneca and Janssen (Johnson & Johnson), which are set to be introduced in Korea. The vaccine from AstraZeneca, in particular, uses the chimpanzee adenovirus-based vector. Although viral vector vaccines are more thermally stable relative to RNA vaccines, they require a cold chain where the temperature is maintained at around 4℃ due to the use of an adenovirus. A viral vector vaccine that has been approved thus far is the Ebola vaccine from Janssen.

The COVID-19 vaccine from AstraZeneca was approved for emergency supply in the UK on December 30 last year. A preliminary review has been conducted by the European Medicines Agency (EMA) since last October. It is currently under review by the MFDS in Korea, as an application for approval was filed on January 4.

The vaccine from Janssen has been undergoing a Phase 3 clinical trial since this past September, but it has not yet been approved anywhere in the world. In Korea, however, a preliminary review is being carried out on a non-clinical study report and the data on its quality as per the application submitted on December 22.

As for COVID-19 vaccines developed in Korea, Cellid [KOSDAQ: 299660] is currently conducting phases 1 and 2 of the clinical trial.

RNA vaccines from Pfizer and Moderna were the first to be commercialized and can be mass produced

An RNA vaccine is a type of vaccine where the antigen gene is injected in the form of RNA to lead to antigen protein synthesis in the body and induce an immune response. RNA, one of the two types of nucleic acids found in the nucleus, plays a role in conveying genetic information and protein synthesis.

Examples of COVID-19 vaccines in the form of an RNA vaccine are the ones from Pfizer and Moderna, which will also be introduced in Korea. Because of the short manufacturing process, these vaccines can be mass produced, but they are relatively unstable as the RNA gets easily broken down by ribonucleases (RNases). Accordingly, they require a cold chain where the temperature can be maintained at around -20℃ or -75±15℃.

RNA-based COVID-19 vaccines were the first to be commercialized in the world.

Pfizer’s COVID-19 vaccine has been approved for emergency use by the UK, USA, Canada, and the World Health Organization (WHO). It has also been conditionally approved by Switzerland and the Europe.

As for in Korea, it is being reviewed by the MFDS, as a preliminary review of the non-clinical study report and clinical trial data was requested on December 18, 2020.

In the case of the vaccine from Moderna, it has been approved for emergency use in the United States and conditionally approved by the EU. In Korea, an application for a preliminary review and approval has yet to be filed.

As for the vaccines developed in Korea, Genexine [KOSDAQ: 095700] and GeneOne Life Science [KOSDAQ: 011000] are in the middle of developing DNA vaccines that are similar to RNA vaccines and conducting phases 1 and 2 of the clinical trials.

Recombinant vaccines boasting excellent safety being tested by Novavax and SK Bioscience

Recombinant vaccines, where the antigen proteins developed by using genetic recombination technology are directly injected into the body to induce an immune response, are one of the most commonly used vaccine platforms. Because the immune response may potentially occur at low levels with just the recombinant antigen proteins, recombinant vaccines require an immunologic adjuvant such as aluminum salts in their formulation. They are known to be highly stable as they have been in application for a long time. Examples of recombinant vaccines include the hepatitis B vaccine and human papillomavirus (HPV) vaccine.

As for recombinant vaccines for COVID-19, an example would be the one developed by Novavax, which has been carrying out a Phase 3 clinical trial since last September. It has not yet been approved for application.

In Korea, SK Bioscience is testing the recombinant vaccine that it has developed in phases 1 and 2 of the clinical trial.

Inactivated vaccines such as the one developed by Sinopharm must meet stringent safety standards

Inactivated vaccines are a traditional type of vaccine platform that induces an immune response by injecting killed (“inactivated”) viruses into the body.

There are a number of vaccines that have been developed using this method. It presents advantages in that it can be developed quickly once the virus has been secured, the manufacturing method is simple, and it boasts excellence in inducing the synthesis of neutralizing antibodies. However, in the case of COVID-19, it requires a production facility of biosafety level 3 (BL3) (biosafety levels ranging from BL1 to BL4) to ensure safe handling of the infectious pathogen.

Examples of inactivated vaccines include the hepatitis A vaccine, poliomyelitis vaccine injection, and inactivated Japanese encephalitis vaccine.

An inactivated vaccine for COVID-19 has been developed Sinopharm based in China, and it was approved for use in China on July 22, 2020.

Source: Yonhap News