JMIR Publications

ABSTRACT

Background:

Social media has become a primary infrastructure for vaccine communication. Personal vaccination disclosures, or first-person announcements of vaccination decisions shared publicly online, represent an underexamined channel through which peer influence may shape vaccine attitudes and behavior. Understanding what individuals disclose when they announce vaccination, and how those disclosures evolve over time, offers actionable insights for designing peer-based communication strategies in future health emergencies.

Objective:

This study aimed to identify the themes present in COVID-19 vaccination disclosures on Twitter, examine how those themes changed across four phases of the U.S. vaccine rollout, and determine which themes were associated with greater public engagement.

Methods:

Guided by the Disclosure Decision Model (DDM), we analyzed 207,647 vaccination disclosure posts on Twitter from December 14, 2020, to January 1, 2022. Posts were identified using a RoBERTa binary classifier (F1 = 0.85) trained on 6,348 human-coded posts. A mixed deductive-inductive coding approach, grounded in the DDM's motivational goals, yielded 11 disclosure themes (Krippendorff's α = 0.72–0.93). Eleven additional RoBERTa classifiers were trained to label themes across the full dataset. Network analysis examined co-occurrence of themes within each rollout phase. Negative binomial regression assessed the association between disclosure themes and an engagement metric (sum of likes, reposts, and quotes), controlling for follower count, media presence, word count, sentiment, and other post-level factors.

Results:

Eleven distinct disclosure themes were identified, including community identity (n=31,258; 15.05%), gratitude (n=28,560; 13.75%), and social benefits (n=27,261; 13.13%). Themes shifted meaningfully across rollout phases: gratitude dominated phase one, community identity rose in phases two and four, and encouraging vaccination became prominent in phase three. Gratitude was associated with a 31% increase in engagement (incidence rate ratio [IRR] = 1.31; 95% CI 1.28-1.34; P<.001), followed by relief (IRR = 1.25; 95% CI 1.20-1.30; P<.001) and community identity (IRR = 1.17; 95% CI 1.14-1.20; P<.001). Political disclosures (IRR = 0.89; 95% CI 0.86-0.93; P<.001) and social benefits disclosures (IRR = 0.88; 95% CI 0.85-0.91; P<.001) were associated with decreased engagement. Each additional theme in a post was associated with a 5.6% increase in engagement (IRR = 1.06; 95% CI 1.05-1.06; P<.001).

Conclusions:

Vaccination disclosures on Twitter were thematically patterned, theoretically interpretable via the DDM, and responsive to changing public health contexts. Identity-based and emotionally resonant disclosures, particularly gratitude and community identity, were most strongly associated with public engagement. These findings provide an empirically grounded framework for designing peer-based vaccine communication strategies that leverage voluntary self-disclosure in future immunization campaigns.