Ordering travellers entering England to isolate on arrival for a fortnight had the desired effect and helped reduce the spread of Covid-19, research showed.
The rules, introduced near the start of the pandemic in summer 2020 was particularly effective for travellers aged 16-20, Cambridge scientists found.
The requirement for people arriving in England to self-isolate for 14 days was introduced on June 8 2020, following the first few months of the pandemic.
It was followed months later when the delta covid wave hit by the even more controversial hotel quarantine scheme which saw passengers arriving from designated 'red list' countries compelled to pay at least £1,750 ($2,840) to stay for 10 days at a government-appointed hotel.
In the original scheme, exemptions were only available for certain people, such as those arriving from destinations where a travel corridor was in place.
The list of travel corridors was repeatedly amended for several months, with popular destinations such as Spain, France, Portugal and Italy added and removed.
The restrictions received fierce criticism from the travel industry due to the impact on demand.
In research published in journal Nature Communications, scientists analysed contact-tracing data from NHS Test and Trace and genome sequences made available through Covid-19 Genomics UK Consortium (COG-UK).
They compared the number of contacts reported per case for international arrivals before they were diagnosed with the virus.
The analysis estimated that travellers with Covid-19 arriving from a location without a travel corridor had an average of 3.5 contacts.
Those who did not need to quarantine had an average of 5.9 contacts, meaning they were more likely to pass on the infection to others.
The number of contacts was highest in the 16-20 age group.
Those who returned from countries with no requirement to quarantine had an average of 9.0 contacts, while those who arrived from a country without a travel corridor typically had 4.7 contacts.
The research was carried out by a team of scientists from the University of Cambridge, the Wellcome Sanger Institute, COG-UK and the UK Health Security Agency.
Dr Dinesh Aggarwal from the Department of Medicine at the University of Cambridge, the study’s first author, 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.”