Types of vaccines
All vaccines contain an active component (the antigen) which generates the protective immune response. Vaccines may also contain additional components.
Vaccines can be broadly classified as live or inactivated. They contain antigen that may be a weakened or killed form of the disease-causing organism, or fragments of the organism. The body responds to the shapes of these antigens, which are very specific. Other ingredients vary depending on both the manufacturing process and the nature of the antigen.
Classification of vaccines
Live attenuated vaccines
Live vaccines are made using ‘wild’ viruses or bacteria that have been attenuated, or weakened, before being included in the vaccine.
After immunisation, the weakened vaccine viruses or bacteria replicate (grow) in the vaccinated person. This means a relatively small dose of virus or bacteria can be given in order to stimulate an immune response.
Live attenuated vaccines do not usually cause disease in vaccine recipients who have a healthy immune system. When a live attenuated vaccine does cause ‘disease’ , e.g. chickenpox vaccine, it is usually more mild than ’wild’ disease.
Live attenuated vaccines given by injection are generally effective following one dose. However, those given orally usually require three doses.
If administered to a person who has an impaired immune system response, e.g. they have leukaemia or HIV infection, or are taking immunosuppressing medications, administration of a live attenuated vaccine may cause severe disease as a result of uncontrolled replication (growth) of the vaccine virus.
Rotavirus, chickenpox, and measles, mumps and rubella vaccines are live attenuated vaccines on the New Zealand Immunisation Schedule. The BCG vaccine is also a live attenuated vaccine however, due to an international shortage of vaccine there is no BCG vaccine stock in New Zealand.
Inactivated vaccines are made using ‘wild’ viruses or bacteria that have been grown in a culture medium and inactivated before being included in a vaccine, or made using a toxin, protein or polysaccharide (sugar) fragment derived from viruses or bacteria (subunit vaccines).
Nothing in an inactivated vaccine is alive. After immunisation, the vaccine antigens cannot replicate (grow) in the vaccinated person or cause disease. This means these types of vaccine can be safely given to a person with an impaired immune system response. However, a person with an impaired immune system response may not develop the same amount of protection after immunisation as a healthy person receiving the vaccine.
Inactivated vaccines usually require multiple doses. Some inactivated vaccines may also require periodic supplemental doses to increase, or ‘boost’ protection against disease.
Hepatitis A, influenza and polio vaccines are inactivated vaccines on the New Zealand Immunisation Schedule. Diphtheria, tetanus, pertussis, hepatitis B, human papillomavirus, Haemophilus influenzae type b, meningococcal, and pneumococcal vaccines are subunit vaccines.
Tetanus, diphtheria and pertussis toxins are inactivated to create toxoids for use in Infanrix-hexa, Infanrix-IPV, Boostrix, and ADT Booster Schedule vaccines.
Polysaccharide (sugar) molecules are taken from the outside layer of encapsulated bacteria such as 23 Streptococcus pneumoniae (pneumococcal) serotypes for use in the Pneumovax 23 special groups Schedule vaccine.
Conjugate vaccines use polysaccharide (sugar) molecules are taken from the outside layer of encapsulated bacteria and join the molecules to carrier proteins. Polysaccharide molecules are taken from Haemophilus influenzae type b (Hib), 13 Streptococcus pneumoniae (pneumococcal) serotypes, and either one of four Neisseria meningitidis (meningococcal) serogroups and joined to carrier proteins for the Schedule vaccines Act-HIB, Prevenar 13, NeisVac-C and Menactra respectively.
The gene segment for a protein from the disease-causing organism that is known to stimulate a protective immune response (protein of interest) is inserted into the gene of another cell, such as a yeast cell. When the cell replicates it has the same shape as the protein of interest. Yeats cells are used for the hepatitis B and human papillomavirus Schedule vaccines Infanrix-hexa, HBvaxPRO and Gardasil, Gardasil 9 respectively.