Editing Serial passage (section)

==Use in vaccines==
One way to attenuate a virus to a host is by passing the virus in a different species.<ref name="woo" />  The idea is that, as a strain of a virus becomes more adapted to a different species, that strain will become less adapted to the original host, thus decreasing in virulence with respect to the original host.<ref name="woo" /> This is the implicit principle that Louis Pasteur was unknowingly making use of when he passed the rabies virus in monkeys and ended up with a virus that was less dangerous to dogs, for example.<ref name="smith" />

The process of serial passage yields a [[live vaccine]].  There are both advantages and disadvantages to this.  Most notably, live vaccines are sometimes more effective and more long-lasting than inactivated or other types of vaccines.<ref>{{Cite web |last=Hunt |first=Richard |title='Vaccines: past successes and future prospects. |url=https://www.microbiologybook.org/lecture/vaccines.htm |access-date=5 May 2014 |website=Microbiology and Immunology On-line.}}</ref><ref name="types">{{Cite web |title=Types of Vaccines |url=https://www.niaid.nih.gov/research/vaccine-types |access-date=5 May 2014 |website=National Institute of Allergy and Infectious Diseases.}}</ref>  However, just as the virus evolved to become attenuated, it may reverse-evolve in the host, leading to infection.<ref name="types" />