A research team headed by scientists of Cambridge University says that the 14-day quarantine measures imposed in summer 2020 on travelers returning to England helped in preventing the spread of the SARS-CoV-2 virus, specifically among 16–20-year-olds.
Airplane wing. Image Credit: Jerry Zhang
Following the first months of the pandemic, in July 2020, the UK government devised new rules for travelers to and from England, to reduce the number of COVID-19 patients coming into the country. Between July 4th, 2020, and February 1st, 2021, the government established “travel corridors” to countries considered to be low in risk for COVID-19, implying that travelers returning from these countries need not quarantine themselves.
But, the majority of people arriving from countries apart from these corridors were asked to quarantine themselves for 14 days at home.
In the study published in Nature Communications, a group of researchers from the University of Cambridge, Wellcome Sanger Institute, COVID-19 Genomics UK (COG-UK) consortium, and UKHSA (formerly Public Health England) analyzed the efficiency of this policy by examining contact-tracing data obtained from NHS Test and Trace and genome sequences that are made available via COG-UK.
The researchers compared the number of contacts reported per case earlier to a COVID-19 diagnosis between travelers returning from a country with a need to quarantine and others who do not require quarantine on return. The team tracked the genomes’ spread from imported cases.
The team detected 4,207 positive COVID-19 cases between 27 May 2020 and 13 September 2020 in England associated with international travel—with more than 51% (half) of all imported cases arriving from either of these three countries: Greece, Spain, and Croatia.
Travelers—with COVID-19 returning from countries—who needed to quarantine themselves had fewer contacts than those arriving from countries that are regarded as the travel corridors, and hence, they were least expected to pass on the infection to others.
With mathematical modeling, they approximate that people traveling from a country needing quarantine had a mean (average) of 3.5 contacts, which is 40% fewer than people returning from a country that does not need quarantine measures (with a mean of 5.9 contacts).
The number of contacts per case was the highest in the 16–20 age group, who had traveled to countries that did not require quarantine, with an average of 9.0. This fell to 4.7 when quarantine was needed, identical to that of other age groups.
Genomic sequencing enabled several unique imported SARS-CoV-2 genomes need be identified, which can be examined to see how extensively the infection had spread. The cluster size—which is the number of related cases of onward transmission—for genomes imported from a country that did not require quarantine upon arrival was considerably higher than for those countries with compulsory quarantine imposed.
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.”
Dr Dinesh Aggarwal, Study First Author, Department of Medicine, University of Cambridge
Dr Aggarwal adds, “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 traveling during this period.”
For the most common destinations, except Spain, the number of imported cases has fallen when the government removed a country from the “safe” list and reestablished compulsory quarantine.
Most of the importations from Greece ended at the end of August and pursued in September, a timespan during which there was no need to quarantine for travelers arriving from the county—this became the cause of the highest imported SARS-CoV-2 cases during the period of research.
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.”
Dr Ewan Harrison, Study Senior Author, Wellcome Sanger Institute
Aggarwal, D., et al. (2022) Genomic assessment of quarantine measures to prevent SARS-CoV-2 importation and transmission. Nature Communications. doi.org/10.1038/s41467-022-28371-z.