scientific basis of vaccines Flashcards
what is attenuation (in vaccines)
making the pathogen harmless but still alive
what is meant by cross-specie protection
similar antigens between pathogens eg antigens of cowpox and smallpox were similar .’. cowpox Ig provide protection against smallpox
definition of vaccine
material from an organism that will actively enhance adaptive (acquired) immunity
what is meant by herd immunity
if majority is immune, there is a resistance to the spread of contagious disease within population .’. provides measure of protection to those who are not vaccinated
what can boost herd immunity
periodic outbreaks of disease in the community
vaccines
how do periodic outbreaks of disease in the community boost herd immunity
improves immunological memory .’. with periodic outbreaks people become naturally immune and don’t spread it i the future
risks of vaccines
measles vaccine - 1/1000 suffer fever/convulsions.
1/400000 suffer meningo-encephalitis
what is active immunity
body’s own B-cells producing antibodies against the antigen and forming memory B-cells that mean there will be a greater response on second exposure.
what is passive immunity
short-term immunity that is induced by receiving antibodies from another source eg mother or medication
what causes active immunity
Natural exposure to antigen (that is carriage)
Getting infected by the pathogen
Being vaccinated
when may we use passive immunity in a clinical setting
for prophylaxis and treatment
how long does adaptive immune system take on primary exposure
5-7 days to start antibody response and 2 weeks to reach full response
what happens in adaptive immune response to primary exposure
first IgM produced by Bcells then class switch -> IgG (more effective) some bcells and tcells become memory cells
how long does adaptive immune system take on secondary exposure
with memory cells circulating, only takes 2 days to mount full immune response. High affinity IgG produced straight away
general principles needed to consider when designing a vaccine
need to induce correct type of response
need to induce immune system in correct place
age when vaccinating
route of inoculation
what is meant by vaccine needing to generate correct type of response
depending on pathogen we may want humoral or cell mediated response
what is meant by vaccine needing to generate response in correct place
diff pathogens reside in diff parts of the body
so for example in influenza virus we induce a mucosal immune response so that sIgA produced and present in mucosal membrane
why must we wait till 9+ months to vaccinate neonates
have maternal IgG (from placenta) and IgA (from breast milk) in their blood .’. mothers Ig will neutralise any antigen present - inc that of the vaccine .’. baby not able to develop immunity
routes of vaccine inoculation
orally (polio)
intradermally (BCG)
subcutaneously (most vaccines)
advantages of oral vaccines
avoid needles, mimics natural route of infection, ensures exposure to large immune surface, produces good sIgA
what is a monotypic antigen
all strains of the antigen are similar .’. when exposed to it once become immune to all strains of the antigen
what is a polytypic antigen
antigens change frequently and different strains have very different antigens.
.’. can be reinfected multiple times - as immune system is naive to the new antigens
what are the three types of vaccine we can give
live, attenuated organism
Killed, whole organism
Sub-unit Vaccines
how may we attenuate an organism
by serial passage (growing it in different environment .’.lower virulence)
recombinant genetics
select natural strains that are attenuated
why do we give killed polio vaccine as opposed to attenuated
polio vaccine type 1 has 57 mutations. however type 2 and type 3 =few mutations.
so t2/3 can easily mutate back to virulent form when replicating. although patient may not show symptoms (due to cross-specie protection) they can shed the virulent polio virus and infect nonvaccinated individuals leading to a new outbreak
issues with using killed, whole organism vaccines
dead organisms= poor cell mediated response (bc dont replicate), likely to cause reactgenicity (may act as allergen, cause toxicity or result in autoimmunity)
how do we deal with the poor cell mediated response in killed, whole organism vaccines
booster injections required in order to get individual up to sufficient immunoprotection
adjuvant may also be used
why do we not need boosters in live attenuated virus vaccines
provide natural boosting as the virus is constantly replicating and growing and presenting its antigen over a period of time.
what is in sub-unit vaccines
contain just individual components of an organism that will drive a good immune response.
eg proteins, toxoids, peptides etc
what is a toxoid
a toxin produced by bacteria that has been inactivated using formaldehyde.
is still antigenic so can be used in subunit vaccines
what happens when we inject a toxoid into an individual
recognised by bcells .’. Ig produced -> inactivates toxin and opsonises it .’. preventing it from damaging body
hence if ever infected again, body already contains Ig against it
