A single on-arrival antigen test is as effective as a ten-day self-isolation period in reducing imported cases of COVID-19, new modelling has revealed. Based on prevalence rates at home and abroad and accounting for quarantine compliance, Oxera and Edge Health find that a single rapid antigen test would be appropriate for arrivals from the majority of countries categorised as medium risk, where there are medium caseloads or lower vaccination rates. Such countries could be designated as ‘amber’ if the UK Government applies a traffic light system for foreign travel to categorise risk.

In evidence submitted to the UK government’s Global Travel Taskforce this week, many of the quick, inexpensive and effective antigen tests are shown to reduce the number of infectious days of an international arrival by 63%. This means that the risk of community transmission from a single test is comparable, if not more effective, to a ten-day quarantine period with no testing, which screens 62% of infectious days and was the UK border policy for countries without travel corridors until 18 January 2021.

The new findings demonstrate how the government’s evidence base has underestimated the effectiveness of a single antigen test, which SAGE previously reported would screen only 11% of infectious travellers.

For higher-risk countries, a two-test strategy could be a viable option as part of a risk-based framework to safely reopen international travel this summer. Using a 72-hour pre-departure antigen test and three-day quarantine with PCR test, 87% of potentially infectious days are screened—just one percentage point lower than a dual-PCR test. Crucially, the new evidence demonstrates that the two-test approach delivers effective levels of screening, while ensuring that the UK can easily track and genome sequence the tests of passengers, mitigating the risk of importing variants of concern.

The government currently mandates a pre-departure test within 72 hours of travel to England and managed quarantine in a hotel for ten days with two PCR tests for anyone arriving from a red list country, at a cost of £1,750. Arrivals from all other countries must quarantine at home for ten days and purchase a £210 travel test package with two PCR tests, for administration on days two and eight of self-isolation.

Michele Granatstein, Partner at Oxera and Head of its Aviation practice, said:

‘The ultimate goal for governments must be to return to frictionless travel between countries that are considered lower-risk. The vaccine roll-out, combined with internationally agreed standards on digital solutions to evidence COVID-status certification, will be intrinsic to that, but people should be able to travel safely, with or without a vaccine.

‘Our analysis of the effectiveness of different quarantine and testing strategies shows that the UK government can safely restart international travel at scale while tailoring test requirements and restrictions on a country-by-country basis.’

George Batchelor, Cofounder and Director of Edge Health, said:

‘When the skies reopen, it’s clear that a proportionate COVID-19 testing regime will remain an effective line of defence to support international travel to and from the UK.’

‘Given the success of the UK vaccination programme, and in line with the UK government’s risk-based approach to the wider economy, any restrictions should be targeted at reducing the potential import of variants of concern. Our modelling demonstrates that a single antigen test for medium-risk countries and dual-test approach for higher risk countries, combined with three-day quarantine, could be an effective strategy to protect public health, while removing the burden of a ten-day quarantine.’

Comparison of dual- and single-testing schemes finds only a marginal benefit, with the two-test approach screening just 5–9% of additional infectious days compared to one test. For example, a single antigen test administered on departure screens 62% of infectious days, while two antigen tests, one administered 72 hours before departure and another on departure, screen 67% of infectious days.

Using 2020–21 data from the USA and the EU, the report also finds that even when COVID-19 prevalence has been higher than the UK, arriving air passengers contribute fewer potentially infectious days into the community per capita compared to domestic infections.

Based on real-world data from 14 December 2020, when prevalence in the USA was the highest that it has been relative to the UK, 10,000 incoming air passengers would have had 79% fewer infectious days than 10,000 individuals in the UK community if a single on-departure antigen test had been administered. The relative risk of importing infections is also expected to decrease further as vaccinations are rolled out domestically and internationally. Around 31 million total Covid-19 vaccine doses have now been administered in the UK, with more than half of adults receiving a first dose.

The report has been submitted to the UK government’s Global Travel Taskforce to inform its new risk-based framework to facilitate international travel.