Attitude inoculation occurs when a subject is exposed to an argument aimed at a pre-existing attitude, then given a refutation to the argument. This bolsters the pre-existing attitude and, in the process, leaves the message receiver prepared to resist future attempts to change their attitude, by having provided counter arguments. There is consensus among scholars and practitioners that attitude inoculation techniques are indeed effective for developing resistance to attitude change (Matusitz and Breen 2013; Niederdeppe, Gollust, and Barry 2014; Pfau et al. 2003) Since its inception, inoculation theory has been studied across multiple fields and has especially been of interest in a marketing context. Several gaps in the current literature are explored in this thesis. The primary problem identified is the lack of longitudinal research conducted to date on the topic of inoculation. Of those studies that do explore longitudinal effects, the vast majority have only done so with periods less than two weeks, despite this being identified as the common point of decay in the effectiveness of inoculation treatments (Banas and Rains 2010). The studies in this thesis are amongst the first to extend past the two-week period. In addition, these studies are also at the forefront of inoculation research in terms of examining differences in argument strength and the effects of moderators such as age, gender, income, and education. Finally, the implementation of a booster message is novel, in that reminder messages (boosters) are only now beginning to be studied, despite being a major unknown factor in the long-term workings of inoculation. In this thesis, the longitudinal impact of inoculation treatments with varied inoculation message strength is explored through multiple survey experiments. The primary analysis method consists of ANOVA with interaction calculations followed by targeted t-tests. The data analysis shows that the effectiveness of attitude inoculation is driven by the inoculation message strength, the passage of various time periods and subject matter relevance. Inoculation success, or lack thereof, is also guided by moderating factors such as additional messages (boosters), gender, age, relationship status, education, and income. From the findings of this thesis, it can be determined that inoculation requires many factors to be in synchrony to be successful. In a marketing setting, attitude inoculation should not be generally applied, instead, specific strategies should be tailored to suit goals. In terms of purchase intent, a strong argument is most effective immediately after an exposure, after which the effect will decay over time, to the point where having applied a strong inoculation is worse than having done nothing at all. Though a weak argument is not initially favorable, over time it is found to be generally more effective than a strong argument. This effect will peak at around two weeks, after which a weak argument will also become less effective than no inoculation. Increasing subject relevance to the target group appears to greatly improve the effects of inoculation. This increased relevance results in some mitigation of long-term decay for strong arguments while significantly improving initial response to weak inoculation treatments for which long-term effects are sustained. Booster (reminder) messages do not appear to increase the effectiveness of inoculation. Very few cognitive effects were found throughout the experiments conducted, however, supporting evidence for identifying emotion as a primary indicator for inoculation response has met predictions.