Jim Bull, Mark Smithson, Scott Nuismer

1. By: Osama Tradat

3.  although transmissible vaccines sound like
somethig out of a science fiction novel,most
vaccines in use and even more being planned
are live capable of replication and possibly
capable of transmission .
 transmissible vaccines could aid the fight
against infectious diseases, and use in
humans may be warranted for populations
that are hard to reach or for epidemics that
are uncontrollable by diret vaccination.

6.  there are two main designs currently in use
with potenial to transmit :

7.  live attenuated vaccines are mutated
genetically weakened version of the diseas
they are designed to protect against.
 they creat a subdued infection that is
otherwise similar to the disease and elicts
immunity just as if you were infected by the
disease..but they dont grow well enough in
you to make you sick

9.  they've been created by growing the disease
virus in an unfavorable environments such as
high temperatures, novel hosts or novel host
cells.
 adaptation to the new environments reduces
viral growth rates in the natural host, so the
vaccines impart immunity without causing
disease.

12. Virus 2
Virus 1

13.  combines two viral genomes, wild virus and
benign virus.
 the benign virus is intact, so it serves as a
vector for the transmission of the disease
antigen. when delivered to the host,the benign
virus multiplies and the host build immunity
against the disease antigens that are encoded
in the vaccine.

14. Disease RVV

15.  there are inherent limitations on the
transmission of each design :
 the genetic weakining of attenuated vaccines
means that they do not replicate well so they
may not be able to transmit well and certainly
not as well as the wild type.
 in contrast recombinant vector vaccines may
often transmit well simply because they have a
fully intact genome of a virus.the vector is
chosen to be benign but it will likely be
transmissible just like its wild type counterpart.
it could be chosen to be more transmissible than
the disease.

17.  if a benign vector virus already exist in a
population, cross immunity between the wild
benign vector virus and the vaccine vector
could prevent the spread of the vaccine.

18.  in addition, recombinant vector vaccines
may not be as immunogenic because they
only contain one or few antigens from the
wild type disease.
 live attenuated vaccines are so similar to the
wild-type disease that they likely induce
more complete immunity.

20.  if attenuated vacc are only a few mutations
different from disease virus as is true for the
current oral polio vacc evolution may easily
and quickly revert them back to the
disease...newer methods of attenuation
could help reduce the likehood of this revers
evolution.

22.  evolution with RVV is less dangerous but still
potentialy problematic this is because
natural selection is likely to favor the loss of
the inserted antigen generating an empty
vector, although the empty vector would be
no more harmful than the natural vector it
would be likely to spread more rapidly than
the engineered vaccine potentialy reducing
the vaccination rate.

23.  These are just a few of the challenges facing
the design and implementation of
transmissible vaccines,solutions to these
problems will emerge from collaboration
among evolutionary biologists,
epidemiologists and genitic engineers