A new UK study has comprehensively analysed the effectiveness of the travel quarantine rules in England during the COVID-19 pandemic.
Experts from the University of Cambridge, Wellcome Sanger Institute, COVID-19 Genomics UK (COG-UK) consortium and UKHSA (formerly Public Health England) conducted the study. The researchers identified that the fourteen-day quarantine rules imposed on incoming travellers returning to England during the summer of 2020 helped stop the dissemination of the SARS-CoV-2 virus, especially among those aged between 16 and 20 years.
The study, which is published in Nature Communications, received funding from Wellcome, UK Research and Innovation, and the COVID-19 Genomics UK (COG-UK) Consortium.
Quarantine rules in England
In England in July 2020, The UK Government established new quarantine rules for people travelling in and out of the country in an effort to reduce the spread of COVID-19. The Government created ‘travel corridors’, between 4 July 2020 and 1 February 2021 to countries that they perceived to have a low risk for COVID-19, meaning travellers returning from the countries did not need to quarantine. However, the vast majority of people returning from countries outside of these corridors were required to quarantine at home for 14 days.
Examining effectiveness
To assess how impactful the quarantine rules were, the team analysed contact-tracing data from NHS test and trace and genome sequences from COG-UK. They compared the number of contacts reported per case before a COVID-19 diagnosis between individuals returning from a country that required quarantine and those from countries that did not. The researchers subsequently tracked the spread of genomes from imported cases.
From this endeavour, the researchers identified 4,207 positive COVID-19 cases in England between 27 May 2020 and 13 September 2020 that were associated with international travel – 51% of the cases came from just three countries, Croatia, Greece, and Spain.
Travellers returning with COVID-19 from countries that required quarantine had fewer contacts than people returning from countries within the travel corridors, meaning they were less likely to pass on the virus. Through employing mathematical modelling, they estimated that people travelling from a country requiring quarantine had a mean average of 3.5 contacts, which is 40% less than someone returning from a country not requiring quarantine rules – an average of 5.9 contacts.
The 16 to 20 age group had the highest number of contacts – an average of 9 – for people who travelled to countries with no quarantine requirement. However, when it was implemented, it fell to 4.7, similar to other age groups. The genomic sequencing performed enabled a range of unique imported SARS-CoV-2 genomes to be identified and monitored to see how far they had spread. The cluster size (the number of related cases of onward transmission) for genomes imported from a country not requiring quarantine on return was substantially higher than those related to countries with quarantine rules in place.
Dr Dinesh Aggarwal, the first author of the study from the Department of Medicine at the University of Cambridge, said: “Although the pandemic now looks very different to how it was in 2020 – with the emergence of new variants offset by increased vaccination – there are still important lessons that can be learned about the effectiveness of quarantine, in particular for future pandemic preparedness.
“Our study shows that while travel restrictions are effective in reducing the number of imported COVID-19 cases, they do not eliminate them entirely. It’s likely that one of the main reasons that quarantine measures helped is that they put people off travelling during this period.”
COVID-19 by destination
Apart from Spain, the number of imported cases was reduced in common destinations when the Government removed a country from the safe list and implemented mandatory quarantine. The majority of importations from Greece arose and the end of August and continued into September – a time when there was no requirement to quarantine for travellers returning from the country. This was the source of the most imported SARS-CoV-2 cases during the study.
Dr Ewan Harrison from the Wellcome Sanger Institute, senior author, added: “Genomics has proven to be an invaluable tool in monitoring how the coronavirus spreads and helping inform infection control measures. By applying it to travel-related cases, it could help governments rapidly refine their travel policies and consider if any quarantine measures are appropriate.”
