The covid-19 vaccination programme, combined with public health measures, have been successful in the UK, leading to restrictions being eased, and plans to reopen international travel. There is however a need for caution. Covid-19 is likely to be endemic globally for the foreseeable future and mathematical modelling scenarios predict potential for a further UK surge of infections later this year. 
As matters currently stand the UK is planning to implement a traffic light system, permitting international travel to resume dependent upon the covid-19 status of destination countries.  Understandably there are pressures to promote travel whether for business or leisure, but it must be appreciated that at the time of writing the UK is an island of low prevalence amid a global surge of covid-19. Risk remains until all nations have emerged from the pandemic through vaccination and other measures.
The Lancet covid-19 Commission Task Force identified risk of spread through air travel as a priority and emphasized that the entire door to door travel process should be evaluated to minimize the risk of transmission.  The All-Party Parliamentary Group (APPG) on coronavirus has identified long queues at airports, failure to separate arrivals from red and amber countries, and fake covid-19 test certificates as significant risks to biosecurity. 
Transmission from asymptomatic travellers may also occur for several days after arrival. Indeed, there are a number of reports of importation of infections from India, despite negative testing prior to boarding. As local indigenous transmission decreases, such imported infections will become the main source of new infections, and border controls will become increasingly important in limiting this risk.
In the UK, border controls are porous. This reflects the political unwillingness to impose stringent controls from early in the pandemic, as well as the inadequate public health measures which have been put in place, for example, the sensitivity and reliability of lateral flow tests; the time and logistics required for more sensitive PCR tests; a large number of exemptions from quarantine, and poor support for those needing to self-isolate or quarantine. 
There is much concern about new covid-19 variants conferring increased transmissibility, pathogenicity, or immune escape, which tend to arise when case numbers are high, although they can also be controlled by effective public health measures. The B.1.1.7 variant which was first detected in the UK, and is up to 30% more transmissible, has become the predominant strain in many countries.  Variants of concern originating in South Africa, Brazil, and now most recently India (currently experiencing a deadly covid-19 surge associated in part with B.1.617) have also in turn been detected in the UK, and indeed B 1.617.2 is currently growing, with the risk of triggering further outbreaks of infection. 
Although such variants could be specifically targeted by updating the new vaccines now being deployed, it will take some time to undertake clinical trials and to scale up manufacture and global distribution. Many variants are already in the UK and we are dependent on high quality surveillance including genomic studies.
Until our vaccination programme is complete, and while there are significant risks of immune-escape variants arising in countries with high transmission, it would be remiss to abandon all attempts to limit new variants being imported into the UK. Chile stands as a salutary reminder of the ease with which covid-19 evades control measures. Chile is currently experiencing a surge in covid-19 infections, despite a successful vaccination programme. They have relaxed social distancing and travel restrictions, and public health experts say that this, combined with more infectious variants has contributed to the surge in infections.  In view of this the APPG on coronavirus has now advised curbs on international travel into the UK beyond the Government’s target date of 17 May 17. 
The new UK Health Security Agency now has a designated role in monitoring emerging infections. Appropriate training in infectious diseases including microbiology/virology is essential. Our global leadership in genomic surveillance (e.g. COG-UK) will be a vital component of this new initiative, but lessons must be learnt to ensure that local expertise is also incorporated.
Most importantly, we must consider the urgent and serious global public health threat of climate change. We should reduce the amount of air travel not only because of covid-19, but also because of the detrimental impact that this has on our climate. This year the UK is hosting the 26th United Nations Climate Change Conference, and expectations for coordinated action to tackle climate change are high. There is an urgent need to do so.
The aviation industry’s current enthusiasm to resume international air travel and overseas holidays, and to expand airports needs to be checked. It flies in the face of the twin needs to control international virus transmission, and tackle the climate emergency and environmental degradation.
Peter Muir, Consultant Clinical Scientist, PHE South West Regional Laboratory Bristol
Deenan Pillay, Professor of Virology, Division of Infection and Immunity, University College London
Jangu Banatvala, Emeritus Professor of Virology, School of Medicine and Dentistry, Kings College London
Competing interests: Deenan Pillay is a member of Independent Sage. Jangu Banatvala is an advisor to SSE (Stop Stansted Expansion)
- SPI-M-O: Summary of further modelling of easing restrictions – Roadmap Step 2
- Prime Minister sets out roadmap to cautiously ease lockdown restrictions https://www.gov.uk/government/news/prime-minister-sets-out-roadmap-to-cautiously-ease-lockdown-restrictions
- THE LANCET COVID-19 COMMISSION TASK FORCE ON SAFE WORK, SAFE SCHOOL, AND SAFE TRAVEL Six Priority Areas FEBRUARY 2021. https://static1.squarespace.com/static/5ef3652ab722df11fcb2ba5d/t/60381fe6acff51132a03173d/1614290919198/Safe+Work%2C+Safe+School%2C+Safe+Travel+%28Feb+2021%29.pdf
- https://appgcoronavirus.marchforchange.uk/curbs_on_international_travel_needed_to_stop_covid_variants_and_prevent_third_wave 30th April 2021
- Muir P, Pillay D, Banatvala J; 2021. Taking back control? Testing chaos at UK borders. https://blogs.bmj.com/bmj/2021/01/08/taking-back-control-testing-chaos-at-uk-borders/
- Chile’s lauded vaccine rollout fails to save it from Covid surge https://www.ft.com/content/89992bc9-051a-42b5-8be0-60edad4165cb