To end the HIV/AIDS epidemic as a public health threat by 2030 [1], we must continue to create local solutions--especially to implement proven strategies directed towards difficult-to-reach subpopulations. To accomplish this, lessons can be learnt from the successes in behavioural change from other disciplines. Behavioural economics is a discipline that studies how individuals make choices within complex contexts, blending insights from psychology with traditional economics of decision-making. A key concept advanced by behavioural economists is that human behaviours are subconsciously influenced by means of choice architecture, which refers to actively designing the environment within which a choice is made to encourage better choices. The ideal choice environment is one that goes with the grain of individuals’ instincts or inherent cognitive and emotional biases to achieve better personal or social goals. The concept of choice architecture was proposed by Thaler and Sunstein [2], and popularized in their best-selling book Nudge. The theory underpinning choice architecture comes from decades of research in behavioural economics and related disciplines. Since 2010, when the UK government established the first Behavioural Insights Unit (aka Nudge units), Nudge units have been commissioned globally to increase the policy relevance of behavioural economics [3]. The challenge to control HIV requires behavioural solutions [4,5]. Perhaps the most important is the tendency for people to give disproportionate weight to immediate and salient outcomes, relative to delayed and more abstract ones. For example, preexposure prophylaxis (PrEP) have costs up front (e.g. daily pill intake and 3-monthly follow-up visits) but the benefits are much later (i.e. prevention of HIV). Another is when the emotionally aroused state before sex affects decision-making, such as safe sex negotiation. To date, there are limited examples for the direct application of behavioural economics into the HIV sector [6], with even fewer published empirical research [7]. A challenge is how lessons from behavioural economics can be more effectively applied by community stakeholders to identify and create nudges to complement their existing programs. To bridge this gap, a crowdsourcing idea to conduct Nudgeathons (a hybrid of ‘nudging’ and ‘hackathons’) was launched [8]. These events are typically conducted over 1--2 days, bringing together a diverse range of stakeholders (many who are new to behavioural science) to create a nudge solution to a specific problem within a time-pressured environment. Nudgeathons have addressed multiple issues (e.g. handwashing among health providers, reducing plastic waste) but to-date, there has not been a Nudgeathon for the HIV/sexual health sector [8]. On 17 January 2020, the creators of Nudgeathon from the University of Warwick (UK) partnered with sexual health experts from Monash University (Australia) to conduct the inaugural Nudgeathon for HIV and sexual health in Melbourne. We brought together 32 participants from different organizations (government, nongovernment organizations, academics, representatives of target populations) with diverse skills (clinicians, epidemiologists, behavioural economists, policy-makers, communication and program design experts, community-advocates). The group learnt about behavioural economics with case-studies of its successful application in various fields. Study investigators allocated participants into four teams ensuring each team consisted of members with different skills. Each team was asked to create nudges for either improving HIV/STI testing or PrEP use among overseas-born gay, bisexual, and other MSM in Australia. We focused on recently arrived (<5 years) overseas-born MSM because of their limited access to the Australian Medicare system (i.e. allowing subsidized access to healthcare) and significant rise in new HIV cases among this population in the past decade (2008–2017) [9]. We used the MINDSPACE framework [10] to identify potential nudges: Table 1 summarizes how this framework was used by Nudgeathon attendees to generate a variety of nudges. These potential nudges will be further developed at a future post-Nudgeathon consolidation workshop to test, implement, and evaluate these in the community. Table 1 - Examples of nudges generated by Nudgeathon attendees to improve regular HIV and sexually transmitted infection (STI) testing and pre-exposure prophylaxis (PrEP) use among overseas-born MSM, using the MINDSPACE framework. Mechanism Example for regular HIV/STI testing Example for access to PrEP Messenger – seen as trusted, expert and authoritative sourceDemographic and behavioural similarities and feeling of the recipient can improve the effectiveness of the intervention. Messages from peers and trusted organization (e.g. community-based organizations) On arrival to Australia, receiving an official welcome letter from the immigration department or educational institutions that also mention available health (including sexual health) services Incentives –shaped by mental biases such as strongly avoiding losses, the value of something depends on where we see it from, overweighting small probabilities, a tendency to allocate different rewards and preferences of more immediate rewards Giving a token to pick up a free HIV self-test kit that must be claimed within 7 days as part of orientation pack for international students (i.e. avoid missing out on getting the kit) Using a time-limited offer to get a quicker and free PrEP appointment, otherwise might have to wait longer Norms – we are influenced by what others do. Social and cultural norms are the behavioural expectations, or rules, within a society or group Messages that most people want to be healthy and look after their health, and that most MSM regularly test for HIV/STI in Australia Show evidence that most people are taking PrEP properly Defaults -- we ‘go with the flow’ of preset options. Defaults are the options that are preselected if an individual does not make an active choice. Defaults exert influence as individuals regularly accept whatever the default setting is, even if it has significant consequences. When someone is identified as high-risk for acquiring HIV (e.g. diagnosed with a sexually transmitted infection on the day) they are automatically enrolled (with option to opt-out anytime) onto a program that will send out a free HIV self-test kit every 3 months Every student gets a lecture and mandatory video at orientation week on sexual health, including information about how to access PrEP and other sexual health services Salience – our attention is drawn to what is novel and seems relevant to us. People are more likely to register stimuli that are novel, accessible (items on sale), simple (a snappy slogan), and relevant We also look for a prominent ‘anchor’ (such as unusual or extreme experiences, price, an advice) on which to base our decisions. Stickers with QR codes in toilets, venues with high throughput of target populations for campaigns using gay slang (e.g. are you a Sticky rice? Potato queen?a) QR code links to website with sexual health information and HIV/STI risk self-assessment tool (e.g. https://ispysti.org/). Banner advertisement on gay dating applications during seasons of risk (e.g. weekends, before holiday) and using the geolocator functionality on apps to automatically find the closest PrEP service to the person or alert them when they are close to a PrEP service Priming – sub-conscious by cues that activate (prime) concepts in our memory. People's subsequent behaviour may be altered if they are first exposed to certain sights, words or sensations (i.e. behave differently if they have been ‘primed’ by certain cues beforehand) Public campaigns using posters and videos to normalize HIV/STI testing with images of overseas born MSM Public campaigns using posters and videos about PrEP with images of overseas born MSM Affect – moods, rather than deliberate decisions can, therefore, influence judgments. People in good moods make unrealistically optimistic judgements, whilst those in bad moods make unrealistically pessimistic judgements After HIV/STI testing, celebrate being STI-free with an indulgent or favourite activity Prompt men to consider PrEP when they are most responsive, for example, arriving in a new country (new opportunities to stay healthy) Commitments – we seek to be consistent with our public promises, and to reciprocate acts. An aspect of commitment is our strong instinct for reciprocity, which is linked to a desire for fairness Make binding commitments with financial punishment for failure (e.g. www.stickK.com) or financial reward for success of regular HIV/STI testing Making a public commitment to others (loved ones, partners, someone whose respect they value) to take PrEP Ego – we act in ways that make us feel better about ourselves. We tend to behave in a way that supports the impression of a positive and consistent self-image. We think the same way for groups that we identify with Framing messages: ‘part of being a good student is looking after your health, don’t let your health interrupt your study’ Framing message: ‘Protect yourself and your partners’; ‘Being sexually empowered makes you a more well rounded person’ Data from [10].a‘Sticky rice’ refers to Asian men who prefer other Asian men; ‘Potato queen’ refers to Asian men who prefer white men.MSM, men who have sex with men; PrEP, pre-exposure prophylaxis; STI, sexually transmitted infection. The success of any HIV prevention strategy is highly dependent on the cooperation and insights from a wide range of stakeholders. Nudgeathons create a microcosm of this and further enriches this process by providing a behavioural framework to understand behaviour and suggest solutions based on these behavioural insights. Nudgeathons are quick and efficient ways to engage multiple stakeholders and develop potential solutions to complex problems, and are feasible to be deployed in developing and low-income and middle-income countries. Learning to better shape the choice environment so that it is easier to stay HIV-negative will be a useful ally in finally ending the HIV epidemic. Acknowledgements We thank the participants of the Nudgeathon. Funding: This study is supported by the Monash-Warwick Alliance for funding the Nudgeathon. JJO (GNT1104781) and EPFC (GNT1172873) are supported by the Australian National Health and Medical Research Council. Author contributions: J.J.O., I.V., D.R., E.P.F.C. conceived the study idea. All authors identified the challenges for the Nudgeathon and ran the Nudgeathon. All authors contributed to the writing of the manuscript and approved the final version for submission. Conflicts of interest There are no conflicts of interest.