Canine distemper virus (CDV), a contagious morbillivirus, infects families in the order Carnivora, including Nearctic river otters (Lontra canadensis). As a preventative measure, vaccinations against CDV are frequently given to mustelids in captive environments. The Pennsylvania River Otter Reintroduction Project (PRORP) used wild-caught river otters to evaluate the efficacy and need for vaccinations against CDV as part of any reintroduction project. The objectives of this study were to: 1) evaluate the prevalence of exposure to CDV in wild river otters, 2) determine the immunologic response of river otters (i.e., seroconversion) after vaccination with a single (primary) vaccine dose compared to a second (booster) dose of Galaxy-D®, a modified live-virus canine distemper (CD) vaccine (MLV CDV), and 3) determine the immunologic response after being vaccinated with a primary vaccination compared to a booster dose of Fervac-D®, an MLV CDV. River otters were injected subcutaneously in the nape of the neck with their designated vaccine. Timeframes for collection of blood samples and/or injection of booster vaccines varied depending on the parameters of PRORP. Ten of the 22 river otters had positive prevaccination titer levels to CD. Both vaccines, Galaxy-D® and Fervac-D®, produced sufficient seroconversion or rise of titer levels (86% and 57%, respectively) to recommend the use of vaccines in wild river otters. Future studies are recommended to evaluate currently produced CD vaccines. Future research should also focus on the number of days required between administration of primary and booster vaccines to achieve sufficient immune response. If only a primary dose is required, then hard-release reintroduction projects for river otters could be recommended. If primary and booster vaccines are required then soft-release reintroduction projects should be recommended. Soft-release projects should include captive management periods that allow for appropriate vaccination intervals and boosters needed to maximize the probability of protection against CDV.