Editing Herd immunity (section)

==Cost–benefit analysis==
Herd immunity is often accounted for when conducting [[Cost–benefit analysis|cost–benefit analyses]] of vaccination programs. It is regarded as a [[Externality#Positive|positive externality]] of high levels of immunity, producing an additional benefit of disease reduction that would not occur had no herd immunity been generated in the population.<ref>{{cite journal|vauthors=Bärnighausen T, Bloom DE, Cafiero-Fonseca ET, O'Brien JC|title=Valuing vaccination|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=111|issue=34|pages=12313–9|date=August 2014|pmid=25136129|pmc=4151736|doi=10.1073/pnas.1400475111|bibcode=2014PNAS..11112313B|doi-access=free}}</ref><ref name=pmid23072714>{{cite journal|vauthors=Deogaonkar R, Hutubessy R, van der Putten I, Evers S, Jit M|title=Systematic review of studies evaluating the broader economic impact of vaccination in low and middle income countries|journal=BMC Public Health|volume=12|pages=878|date=October 2012|pmid=23072714|pmc=3532196|doi=10.1186/1471-2458-12-878 |doi-access=free }}</ref> Therefore, herd immunity's inclusion in cost–benefit analyses results both in more favorable cost-effectiveness or cost–benefit ratios, and an increase in the number of disease cases averted by vaccination.<ref name=pmid23072714/> Study designs done to estimate herd immunity's benefit include recording disease incidence in households with a vaccinated member, randomizing a population in a single geographic area to be vaccinated or not, and observing the incidence of disease before and after beginning a vaccination program.<ref name=pmid23357859>{{cite journal|vauthors=Jit M, Newall AT, Beutels P|title=Key issues for estimating the impact and cost-effectiveness of seasonal influenza vaccination strategies|journal=Human Vaccines & Immunotherapeutics|volume=9|issue=4|pages=834–40|date=April 2013|pmid=23357859|pmc=3903903|doi=10.4161/hv.23637}}</ref> From these, it can be observed that disease incidence may decrease to a level beyond what can be predicted from direct protection alone, indicating that herd immunity contributed to the reduction.<ref name=pmid23357859/> When [[#Serotype replacement|serotype replacement]] is accounted for, it reduces the predicted benefits of vaccination.<ref name=pmid23072714/>