This technology is also used in vaccines against hepatitis B and some influenza vaccines.
Virus-like Particles (VLP)
These vaccines contain viral proteins that are arranged to resemble a viral particle, but the virus-like particle cannot replicate. Different cell types can be used to produce these vaccines. The virus-like particles cannot cause disease, but the immune system is stimulated to induce antibody responses that can contribute to combatting covid-19 in the event of a later infection.
This technology is also used for the vaccine against HPV (human papillomavirus).
Viral vectors – non-replicating
These vaccines are not made up of the covid-19 virus but use a different virus as a vector. The DNA genome in the viral vector is changed so that the viral vector cannot replicate, and its DNA encodes the spike protein of the covid-19 virus. The covid-19 vaccines approved so far that use this technology, use a common cold virus (from the adenovirus family) as a vector.
When the viral vector enters the host cell, the host cell machinery will use the information encoded in the DNA to produce the spike protein from the virus that causes covid-19. The spike protein does not cause disease, but the immune system will generate antibodies to the spike protein as well as prepare immune cells (T-cells) to combat covid-19 in the event of a later infection.
Viral vectors for these vaccines are defined as gene modified organisms (GMO). Research has not indicated that these viral vector vaccines have the ability to induce changes in the genes of the vaccinated individual. As for all other vaccines, they are only transiently present in the body before they are broken down and removed by the immune system.
This technology has been used for some Ebola vaccines.
Approved covid-19 vaccines and vaccine candidates under evaluation that use non-replicating viral vectors:
mRNA vaccines
These vaccines contain messenger RNA (mRNA) which, once in the cell, can be used to make the spike protein of the virus causing covid-19. The mRNA is ‘packaged’ into small lipid particles to help the mRNA enter host cells. The cell's protein synthesis machinery is then used to make the spike protein. The spike protein does not cause disease, but the body will generate antibodies against the spike protein and prepare immune cells (T-cells) to combat covid-19 in the event of a later infection.
This technology is new which is why vaccines based on this technology have not been approved previously.
Approved covid-19 vaccines that use mRNA technology:
DNA Vaccines
These vaccines contain DNA (*) which codes for the spike protein of the virus causing covid-19.
The host cell uses the information encoded in the DNA to produce the spike protein. The spike protein does not cause disease, but the body will generate antibodies against the spike protein and prepare immune cells (T-cells) to combat the virus causing covid-19 in the event of a later infection.
(*) The virus causing covid-19 (SARS-CoV-2) is an RNA virus. The DNA that is used in the vaccine is cDNA (complementary DNA).
This technology is new which is why vaccines based on this technology have not been approved for use in humans previously.
