The importance of air travel in facilitating the long-distance spread of COVID-19 is undisputed 1–6. For example, it is now well established that UK citizens returning from mainland Europe (e.g. Italy, Spain and France), rather than China, were primarily responsible for initially introducing SARS-CoV-2 into the UK 7. Based on sequencing it has been estimated that at least 1300 independently-introduced transmission lineages of the virus were introduced to the UK in early 2020, leading to the first wave of COVID-19 7. Based on this, we estimate that infected passengers entering the UK represented ca. 0.02% of the 8 million passengers arriving during this period. This was, however, notably lower than the estimated 1.3% of infected international passengers that left Wuhan at the start of the pandemic and which fuelled the global spread of the disease 8. At the beginning of the second COVID-19 wave in Europe, in-flight transmission of SARS-CoV-2 between passengers was also documented in a flight from Greece to Ireland, where the attack rate was 10–17% 9. This transmission occurred despite the use of face coverings and the implementation of social distancing measures. A range of modelling and epidemiological case studies has also confirmed that one infected person on a flight could transmit the disease to other passengers throughout the plane 10. This is not helped by the close proximity of other passengers, intrinsic air circulation patterns and closely confined and high frequency use toilet facilities. The potential for importing and transmitting SARS-CoV-2 on aircraft mirrors the findings for other respiratory viral diseases (e.g. influenza; 11,12). In addition, the potential for transmission within crowded airport terminals has also been demonstrated for other respiratory pathogens (e.g. adenovirus; 13) suggesting that a single individual carrying the disease may infect multiple people all travelling to different destinations.
Although closure of international flights has inevitably helped contain the spread of the disease, it has come at a substantial cost 14–16. For example, COVID-19 restrictions on air travel has led to major economic and job losses in many countries 17,18. There is therefore an urgent drive from the travel industry to re-open international air routes post-pandemic. However, this must be done in a socially responsible, practical and economic way that will ensure protection of public health. Key to this is effective disease control and surveillance. This clearly requires the development of practical, cost-effective and socially acceptable surveillance technologies but also necessitates a good knowledge of individual attitudes to COVID-19 and their behaviour before, during and after air travel. From one survey of the public acceptance of quarantining measures it was concluded that public support is vital for any program involving quarantine and isolation 19. Further addressing challenges and barrier to enlist the support of the public is essential to optimize compliance 20,21.
Appraisal of airport entry screening measures have shown that it is highly resource demanding 22 and often ineffectual 4,23. Although a range of strategies are now in place for national disease surveillance (e.g. contact tracing, self-reporting apps, targeted and untargeted swab, testing, seroprevalence), we still lack ways to reliably estimate rates of disease entry from overseas travellers. Based on the known trans-national importation of new variants of SARS-CoV-2 into the UK (e.g. beta, gamma, theta, omicron), it is clear that current surveillance strategies remain inadequate both at the point of departure and the point of entry. This is either because (i) current technologies lack scientific credibility (e.g. thermal imaging gates), (ii) are not cost-effective for mass deployment, (iii) are subject to error (e.g. lateral flow devices, swab testing), (iv) fail to capture recently acquired infections (e.g. those acquired within hours of departure), (v) are not available at the point of departure, (vi) cannot capture infections acquired during travel (e.g. in transit lounges or on the flight), or (vii) solely rely on self-reporting which fails to capture asymptomatic, pre-symptomatic, mildly symptomatic individuals and those knowingly concealing symptoms 24,25. This is supported by an ECDC study which estimated that ca. 75% of infected individuals from China arrived at their destination undetected 26. To help mitigate this, many countries have implemented policies of quarantining passengers for 10–14 days upon arrival.
Clearly, self-quarantining relies on individual compliance if it is to be effective. In particular this includes obedience and/or agreement to follow quarantining polices. It has been suggested that obedience involves respect of implicit and explicit rules and that is a socially learned behaviour 27. In contrast, disobedience is suggested to be a behaviour where an individual takes a conscious stance against formalized laws or implied social norms 27. Therefore, if individuals refuse to comply with quarantining policies, due to obedience being a learned behaviour from childhood, then these individuals may also be less likely to follow other health advice put forward to mitigate the spread of COVID-19 (e.g. mask wearing), posing further risk to themselves and others.
With a focus on UK air travellers and those that have flown during the pandemic, the primary aims of this study were to evaluate how human behaviour associated with travel can increase the risk of spreading COVID-19. We aimed to (i) evaluate passenger knowledge of COVID-19 symptoms, (ii) their attitudes to catching COVID-19, (iii) evaluate their likelihood of returning back to the UK if they, or a member of their family, were ill, (iv) evaluate their perceived safety during recent air travel, and (v) the likelihood that they would self-quarantine for the full period on return to the UK.