Purpose High dispositional optimism is often associated with people engaging in behaviour that has adverse effects on their health such as smoking. This study aims to investigate people’s intention to adopt preventive health behaviour by observing the effectiveness of anti-smoking ads during the ongoing coronavirus (COVID-19) pandemic. Design/methodology/approach Two studies have been carried out, first with a UK sample and second with the US sample. The studies examined the effectiveness of anti-smoking ad (appeal: high fear vs low fear), smoking behaviour elicited perception of vulnerability to COVID-19 and dispositional optimism on lowering people’s urge to smoke. Findings The study findings revealed a high fear appeal ad is more effective in lowering people’s urge to smoke. However, this association is significantly mediated by perception of vulnerability to COVID-19. Further, high dispositional optimism was found to moderate the effect of the anti-smoking ad on the perception of vulnerability to COVID-19, although a comparatively smaller effect was observed for the UK sample. Finally, high dispositional optimism significantly moderated the mediation of vulnerability to COVID-19 on lower urge to smoke only for the US sample. Originality/value The study highlights a need for a greater collaborative effort by the public, government, firms in the business of nicotine replacement solutions, socially responsible cigarette and tobacco manufacturing firms and health agencies that may lead to increased preventive health behaviour during the ongoing pandemic.