The types of vaccines include: whole virus (inactivated and live-attenuated) vaccines; genetic material RNA (mRNA) vaccines; subunit; recombinant; polysaccharide and conjugate vaccines; toxoid vaccines; and viral vector vaccines.
Many conventional vaccines use whole viruses to trigger an immune response. Live attenuated vaccines such as the measles-mumps-rubella (MMR) vaccine use a weakened form of the virus that can still replicate but are unlikely to cause disease. Inactivated vaccines such as hepatitis A use viruses whose genetic material has been destroyed (sometimes referred to as ‘killed’) so they cannot replicate.
Nucleic acid vaccines use genetic material – either DNA or some forms of RNA – to provide cells with the instructions to make the antigen. Some of the new COVID-19 vaccines use messenger RNA technology.
Viral vector vaccines also contain genetic material that give our cells instructions to produce antigens. They use a harmless virus as the ‘vector’ or carrier – which is different from the one the vaccine is targeting – to deliver these instructions into the cell. An example is the rVSV-ZEBOV Ebola vaccine.
Subunit, recombinant, polysaccharide and conjugate vaccines
These use one or more antigens – such as a protein or sugar – to trigger an immune response to the germ. Conjugate vaccines for example combine a weak antigen carried by a strong antigen to ensure a stronger immune response. An example is the recombinant hepatitis B vaccine containing a surface antigen.
Toxoid vaccines, such as the tetanus vaccine, use controlled amounts of a toxin made by the germ. They create immunity to the disease-causing parts of the germ instead of the germ itself. That means the immune response is targeted to the toxin instead of the whole germ.