Similarly, the interaction between the dynamics of transmission and
protective immunity have been critical in the evaluation of strategies for switching
from oral polio vaccine (OPV) to inactivated polio vaccine (IPV)Tebbens 2014. OPV produces a stronger protective immune
response, including secretory IgA at the mucosal surface, and is shed into the
environment leading to passive environmental vaccination Hird 2012. However, the live-attenuated virus used in
OPV can, rarely, result in disease symptoms and reversion to wild-type
virulence Hird 2012. IPV does not present a risk
for the emergence of vaccine-derived polioviruses, but at the cost of weaker
immunity. The risks of OPV outweigh
those of IPV once disease rates drop sufficiently, though the specific rates at
which this transition occurs depend on the local transmission and demographic
context. Dynamic models are useful to identify this phenomenon in the first
place, and combined with local surveillance and demographic observations can be
of practical use to identify and evaluate locally tailored strategies for
switching to IPV.