VACCINES
PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU.
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Objectives Students should be able to:
• summarise the mechanisms of primary and secondary immune responses to virus infections and to vaccines. • compare and contrast different types of vaccine with some veterinary examples. • describe the influence of maternal antibody on vaccination outcome. • list some of possible reasons for the failure of vaccines to protect against disease.
Vaccination involves setting up memory to the virus infection such that a high level of cytotoxic T cells (Tc) and IgG are activated in 1-2 days instead of 4-10 days. These curtail the infection before lesions develop. IgA/IgG at mucosal surfaces are also useful to neutralise virus before entry but is difficult to achieve except by mucosal live vaccines.
The mechanisms of recovery from a primary infection will first be reviewed
The mechanisms of recovery from a primary infection will first be reviewed (cont.)
The mechanisms of recovery from a primary infection will first be reviewed (cont.)
Reasons for a failure to recover
Vaccination
Types of field vaccine Maternal antibody and vaccination Reasons for vaccine failure
Types of field vaccine:
1) live (attenuated) 2) inactivated 3) subunit 4) recombinant 5) DNA vaccines, research
1) Live (attenuated)
1) Live (attenuated)
(cont.)
2) Inactivated vaccines
3) Subunit vaccines
4) Recombinant live vaccines
5) DNA vaccines, research
Maternal antibody and vaccination
Maternal antibody and vaccination
(cont.)
Reasons for vaccine failure.
SUMMARY
Vaccines are used for endemic diseases which may then become so rare vaccination can cease Vaccines induce memory for Tc and VN IgG/IgA but without the risk of disease. Most commercial vaccines are either inactivated or liveattenuated with the exception of the recombinant FeLV from E.Coli. Inactivated vaccines are more expensive to produce and often administered with adjuvants Vaccines must be quality controlled The vaccination programme must allow for maternal antibody Vaccines can fail, most usually because of new challenge viruses with altered antigens or increased virulence.