Vaccine terms

Adjuvants: Antibody enhancing agents. Chemical substances which are supposed to enhance the immune response to the vaccine.
Heat or chemically treated.
Conjugated: segments of one antigen are linked with those of another antigen. Eg Hib antigen & diptheria antigen.
Killed or inactivated vaccines:
Live vaccines:

diploid cells (aborted fetal tissue)

Cell lines (Human fetal):
MRC-5 (Medical Research Council 5): MRC5 originates from the lung tissue taken from a 14 week male fetus aborted for "psychiatric reasons" from a 27 year old woman in the UK in the 1970s

WI-38: WI -38 originates from a female fetus aborted for "psychiatric reasons" in the 1960s. These abortions were not done for the purpose of producing vaccines


A toxoid is a modified bacterial toxin that has been rendered nontoxic but retains the ability to stimulate the formation of antibodies.

13) Attenuation

(a) Attenuation is a decline in virulence imposed on a pathogen by growing the pathogen under conditions that decrease its adaptation to growth on a given host; this is often done by growth in tissue culture or in otherwise non-host species

(b) That is, by increasing a pathogen’s adaptation to one condition (e.g., tissue culture), the pathogen’s adaptation to another condition (e.g., us) may be reduced

(c) Attenuation is often employed in the development of live vaccines (e.g., Sabin oral polio vaccine)

Live vaccine (live-attenuated vaccine)

(a) Live vaccines result in infection but not disease, and confer the most long-lasting immunity

(b) Live vaccines typically are attenuated so that while they can still cause infection, they have a reduced propensity to cause disease

Live Attenuated Vaccines

Most of the live attenuated vaccines in use today are derived from serial passage in cultured cells, including human diploid cells (e.g. fetal lung tissue, other fibroblasts), monkey kidney cells, and chick embryos, among others. Adaptation of the virus to growth in the cultured cells is accompanied by a gradual loss of virulence for the natural host. The neurovirulence of the attenuated virus is tested in mice and primates before conducting trials with humans. This procedure relies on the accumulation of point mutations to confer avirulence; however, more exact mutations can be attained through genetic engineering. Temperature sensitive mutants, deletion mutants, site-directed mutatgenesis, and live recombinant viruses are all methods that are commonly employed to achieve viral attenuation. These vaccines generally possess the following properties:

derived from wild virus
attenuated through repeated culturing or recombination
must replicate to be effective
produces strong cellular immune response similar to natural infection
severe reactions possible in immunosuppressed vaccinees
can revert to pathogenic form
require only one or two doses
interference from circulating antibody
require refrigeration or lyophilization (freeze-dry)