Evidence-like but misleading: Framing and engagement in measles vaccine discourse on Substack

Background

Measles remains one of the most transmissible vaccine-preventable diseases, with recent outbreaks reflecting declining immunization uptake and growing distrust in public health institutions. Online platforms increasingly shape perceptions of disease risk and vaccine safety. Substack, a newsletter-based platform with minimal editorial oversight and direct audience reach, has emerged as a prominent venue for measles and vaccination discourse, where expert analysis, personal narratives, and unverified claims circulate.

Methods

Guided by the Health Belief Model (HBM), including perceived susceptibility and severity, perceived benefits and barriers to the measles-mumps-rubella (MMR) vaccine, cues to action, self-efficacy, as well as message framing, we conducted a content analysis of N = 700 Substack posts referencing measles and the MMR vaccine.

Results

Over half of posts (56%) expressed vaccine-critical positions, and 45% portrayed measles as a benign childhood illness rather than a highly contagious and potentially severe infection. Among vaccine-critical posts, 73% endorsed conspiracy narratives or expressed distrust in public health and medical providers, and 41% mentioned autism as a side effect of the MMR vaccine. Posts minimizing measles severity and susceptibility and emphasizing barriers to vaccination generated higher engagement than those emphasizing disease risk and vaccine benefits. Thematic framing was used in 85% of posts, including most vaccine-critical content.

Discussion

Engagement patterns indicate that content reducing perceived threat while amplifying barriers is more likely to spread, aligning with HBM pathways linked to lower uptake intentions. The widespread use of thematic framing, which is typically associated with evidence-based communication, may enhance perceived credibility of vaccine-critical messages and broaden their reach, underscoring the need for public health strategies that address both message content and structure.

Key messages

• Posts minimizing measles risk and emphasizing vaccine barriers generate higher engagement, suggesting content that lowers perceived threat is more likely to spread online.

• Vaccine-critical content often uses thematic, evidence-like framing, which may boost credibility and reach, highlighting the need for public health strategies addressing both content and format.