How does the COVID-19 vaccine work?

The vaccines used currently in Finland against COVID-19 are so-called mRNA vaccines, adenoviral vector vaccines and a protein-based vaccine. All vaccines provide approximately equally efficient protection against the coronavirus disease.

mRNA and adenoviral vector vaccines do not contain the virus causing the coronavirus disease or its elements. The protein-based vaccine does not contain live viruses that cause coronavirus disease.

The abbreviation RNA refers to ribonucleic acid which is located in cells. The messenger RNA code instructs the cell to produce the proteins that are indispensable for the body. 

The mRNA vaccines contain messenger RNA (mRNA) whereby the muscle cells in the point of injection are triggered to produce the active ingredient of the vaccine.  In case of COVID-19 vaccines, this is the surface protein of the COVID-19 virus. When the surface protein is dosed into the body, the body starts to produce antibodies against it, i.e., it starts to build protection against the potential COVID-19 virus. In addition to the messenger RNA, the vaccine contains water, salts, sugar and lipids.

Adenoviral vector vaccines also induce the vaccinated person’s own muscle cells to produce the COVID-19 virus surface protein. The operative mechanism is different – the adenoviral vector vaccines contain a gene copied from the COVID-19 virus, and the code contained in it starts to produce the COVID-19 virus surface protein, the so-called spike protein, in the cells. 

In vaccines, this gene is included as a part of the genotype of a harmless viral vector, the adenovirus. Correspondingly to mRNA vaccines, the adenoviral vector vaccines also contain water, salts, sugar and lipids, and do not contain a reproductive COVID-19 virus.

The active substance in the protein-based vaccine is a laboratory-produced SARS-CoV-2 virus spike protein. The body recognises the spike protein in the vaccine as foreign and starts to defend itself against it by producing antibodies and activating T-cells (defender cells). If coronaviruses enter the body later on, the T-cells recognise them and activate other parts of the body’s immune system.

The other protein-based vaccine excipients are salts, polysorbate 80 and water, together with small amounts of other substances that maintain the correct composition for the vaccine. The vaccine contains also an adjuvant called Matrix-M which is a natural saponin-based adjuvant. This adjuvant is used to boost the protection against coronavirus provided by the protein-based vaccine.


Further reading


Page published 28.4.2021
Page edited 21.12.2022