Purpose Social media, such as Twitter, has become the first and the most frequent place to visit in order to gain information and establish situational awareness in emergencies and disasters. The purpose of this paper is to examine public opinion on Twitter in different disaster stages using the case of Hurricane Irma. Design/methodology/approach More than 3.5m tweets capturing the entire disaster lifecycle were collected and analyzed. Topic modeling was used to generate topics at each disaster stage based on Fink’s (1986) four-stage model of crisis and disaster: prodromal, acute, chronic and termination stages. Findings The results revealed that media reliance varied across different stages. All topics in the prodromal stage were associated with the early warning and real-time news. The topic of lessons learned from Hurricane Harvey was the most popular at this stage. The acute stage recorded the highest number of daily tweets. The most popular topic was the safety of people and animals. In the chronic stage too, the safety of people and animals remained a major concern. Heroic and anti-social behaviors also received substantial attention. In the termination stage, climate change was the most frequently discussed topic. Politics-related discussions were heated. Originality/value The results extended and enhanced the four-stage model of crisis and disaster. These findings can help government agencies and crisis managers address audience needs effectively at various crisis stages in a timely manner.

Online anti-vaccine articles contribute to the anti-vaccine movement, which leads to recent outbreaks of vaccine-preventable diseases. Previous studies indicate that anti-vaccine articles are easy to read and understand, which may increase their abilities to engage viewers. The present study aims to examine if readability levels are related to engagement. Using combination of terms to search for vaccine articles in Google in May 2017, this study examined 541 pro-vaccine online articles with a total of 508,571 words and 382 anti-vaccine articles with a total of 843,805 words. Almost all vaccine articles exceeded the American average reading comprehension level. No significant difference in readability was found between pro- and anti-vaccine articles. Pro-vaccine articles that could only be understood by college graduates were less engaging than those with lower readability levels. No significant relationship between anti-vaccine articles’ readability and engagement was discovered. Different vaccine topics had different readability and engagement levels, which implied that certain combinations of themes and readability levels could enhance the health messages’ persuasion effect. Recommendations for designing effective health messages are provided.

Flu remains a prevalent public health issue and the flu vaccine uptake remains low. This study examined the behavioral consequences of first-and second-level agenda setting by testing the effects of exposure to flu-related news coverage and different frames on flu vaccine uptake, while controlling for confounding sociodemographic factors, utilizing computational methods. Findings suggested that the media effects on children and adult influenza vaccine uptake differed. The frame of influenza caused deaths/illnesses stories was the only media frame that positively predicted flu vaccine uptake among children. Four frames, including influenza caused deaths/illnesses stories, flu prevention tips, things to know about flu vaccine, and public accountability positively predicted flu vaccine uptake among adults. Exposure rate negatively predicted flu vaccine uptake among adults. A few sociodemographic factors impacted flu vaccine uptake. Results also revealed the most and least exposed frames and state exposure rates to flurelated news stories.

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