A randomized assessment of the impact of 'Those Nerdy Girls' newsletters on adult vaccination outcomes.

Adult vaccine-preventable infectious diseases contribute substantial burden each year, and vaccine uptake remains suboptimal. As digital health communication grows, digital newsletters may represent a scalable, low-cost tool to promote vaccination. We conducted a randomized prospective study to evaluate the impact of digital newsletters on subscribers' knowledge, attitudes, and behaviors regarding four adult vaccines: respiratory syncytial virus (RSV), influenza, shingles, and COVID-19. Between November 2023 and January 2024, half of subscribers to the Those Nerdy Girls (TNG) Substack newsletter received additional vaccine-focused newsletters, while the other half received only the standard twice-weekly newsletters. Pre- and post-intervention online surveys assessed vaccine knowledge, attitudes, and behaviors among adult subscribers who consented to participate. Across 1,327 pre-intervention and 1,208 post-intervention participants, knowledge gains were observed for RSV and shingles vaccines in the intervention group compared with controls, while knowledge of influenza and COVID-19 vaccines did not improve. Attitudes toward vaccination were generally positive at baseline and showed no significant intervention effects across vaccine types. Likelihood of vaccination increased for influenza, COVID-19, and RSV overall during the study period, but only influenza vaccination showed a significantly greater increase in the intervention group relative to controls. No significant effects were found for shingles vaccination. These results indicated that digital newsletters can improve knowledge and, in some contexts, support uptake, but knowledge gains did not consistently translate into changes in attitudes or behaviors. Findings highlighted the limitations of knowledge-deficit models for adult vaccination promotion. Digital newsletters should be considered as one component of broader public health strategies, particularly when paired with approaches that address logistical access, trust, and social norms.