Current advice from the UK government states that after arriving back in the UK, individuals must self-isolate for the first 14 days, unless they have returned from a country that is on the exempt list.1
Unfortunately, due to the varying levels of COVID-19 outbreaks, the list of exempt countries can change rapidly, leading to chaotic scenes at airports and ferry terminals, as holiday-makers rush home in an effort to beat the deadline for the introduction of the quarantine. It has been argued that the present quarantine measures are having a potentially devastating effect on the UK’s economic recovery, with many people who have travelled abroad, unable to return to work for two weeks. Airline bosses have even called for both airport testing for COVID-19 and a reduction in the quarantine period. But what is so special about the 14-day quarantine period and could this be shortened and still remain effective?
Early work from China suggested that the incubation period for COVID-19 was around 5 days and that individuals should be isolated (or quarantined) for up to 14 days.2 Routine COVID-19 testing relies upon reverse transcriptase polymerase chain reaction (RT-PCR), which seeks to ‘rule out’ infection and hence the need for quarantine measures. Consequently, it has been proposed that RT-PCR testing at an airport prior to departure and upon arrival back in the UK could obviate the need for self-isolation.
In fact, some countries have already instigated a policy based around this model of testing. For instance, travellers from Singapore to China (and vice versa) have to undertake a RT-PCR test within 48 hours of departure and obtain a certificate proving a negative test result. Upon arrival, a second RT-PCR test is required, and travellers are required to remain in designated locations for one or two days until the test result is available. If this second test is negative, they are permitted to travel onwards to their destination without further quarantine.3
However, a potential problem with testing people either prior to departure or even upon arrival, is that the RT-PCR test is subject false negatives, that is, where the test indicates that a person does not have the virus when, in fact, they are infected. The probability of a false-negative depends, to a large extent on time when the test is performed in relation to an individual’s period of infection. Recently, Kucirka et al4 examined the predictive value of RT-PCR tests based on a total of 7 studies that included 1330 patients. They examined the false-negative probability of the test over the 4 days of infection before the typical time of symptom onset (day 5). The results showed that the probability of a false-negative result decreased from 100% on day 1 to 68% on day 4 and that on the day of symptom onset, the median false negative rate was 38%. In important finding from the study was that the false-negative rate was minimised 8 days after exposure, in other words, 3 days after the onset of symptoms. Despite its use in several countries, these data suggest that airport testing might actually miss many infected people. It has also been the argument advanced by the UK government as to why airport testing is not being used. Could this approach be used in the UK and to what extent would it reduce the potential spread of COVID-19?
Modelling of testing strategies
To better understand the effectiveness of double-testing, studies have modelled the effects double testing combined with different levels self-isolation. Public Health England undertook a study to estimate the effectiveness of double testing incoming travellers to the UK and hence the need for the 14 day quarantine period.5 The modelling assumed that all individuals would undergo testing upon arrival into the UK and that they would be quarantined for differing periods of time before undertaking a second test. The model also made the assumption that all individuals were infected prior to boarding at their destination and estimated the effect of differing flight times (for example, either short/medium/long). The modelling determined the probability of infected individuals gaining entry to the UK with a base case of no self-isolation or additional testing, that is, they were only tested on arrival.
With just a single testing performed at the airport, the analysis predicted that 3% of positive cases would be identified after a short haul (3 to 5 hours) flight and 7% after a medium haul (7 to 9 hours) flight. Further scenarios are shown in Table 1.
The results in Table 1 clearly show that a 7-day period of quarantine would enable the detection of 85% of positive cases. However, quarantining for a total of 10 days was estimated to provide virtually the same detection rate (96% vs 98%) as the current 14-day requirement. Similar findings have been produced by other study. In an analysis by Clifford et al,6 it was found that a quarantine period of at least 5 days, with a single RT-PCR test on the final day, would reduce the number of infectious individuals entering the UK by over 80%. An 8-day quarantine (with 1-day delay for the test results) would reduce the number of infectious individuals by 94% which is approximately the same as the current 14-day quarantine.
In summary, in an effort to prevent the import of new COVID-19 cases, there is a need to ensure some form of quarantine and testing for individuals arriving in the UK, especially given that fact that the rates of infection can rapidly change different several countries. Modelling studies suggest that reducing the period of self-isolation to 8 days in combination with two RT-PCR tests is a potentially effective and alternative strategy to the current blanket 14-day quarantine rule. The current requirement for 14-day quarantine period without testing is felt to be having a negative impact on the UK economy. Therefore, although testing all arrivals is a labour-intensive endeavour, any approach that both minimises the risk for the transmission of COVID-19 and lessens the effect on an already damaged economy should be carefully considered given the ongoing nature of the current pandemic.
It is also important to note that the 14-quarantine period applies even if an air traveller makes a short stopover, for instance, if they are changing flights, in a country that is not on the exempt list. This is because of the potential risk posed by other passengers who might join the flight. In such instances, the period of self-isolation is reduced to 10 rather than the usual 14 days. Moreover, the quarantine rules don’t apply to when travelling within ‘common travel areas’, for example, to Jersey, Guernsey, the Isle of Man and Ireland. Finally, it seems that the restrictions do not apply to everyone and individuals from specific professions are exempt. This includes members of diplomatic missions and consular posts in the UK, Eurotunnel workers and those engaged in essential or emergency work, airline pilots and crew. A full list can be found on the government website.7
- Coronavirus (COVID-19): how to self-isolate when you travel to the UK. Gov.UK. www.gov.uk/government/publications/coronavirus-covid-19-how-to-self-isolate-when-you-travel-to-the-uk/coronavirus-covid-19-how-to-self-isolate-when-you-travel-to-the-uk (accessed October 2020).
- Li Q et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia. N Engl J Med 2020;382:1199–207.
- Ministry of Foreign Affairs. Joint press statement by Ministry of Foreign Affairs and Ministry of Trade and Industry on the Singapore-China fast lane for essential travel. www.mfa.gov.sg/Newsroom/Press-Statements-Transcripts-and-Photos/2020/06/20200603-SG-CHINA-Fast-Lane-Essential-Travel (accessed October 2020).
- Kucirka LM et al. Variation in false-negative rates of reverse transcriptase polymerase chain reaction-based SARS-CoV-2 tests by time since exposure. Ann Int Med 2020; doi:10.7326/M20-1495.
- Public Health England. Investigation into the effectiveness of ‘double testing’ travellers incoming to the UK for signs of COVID-19 infection. Gov.UK. www.gov.uk/government/publications/phe-investigation-into-the-effectiveness-of-double-testing-travellers-incoming-to-the-uk-for-signs-of-covid-19-17-june-2020 (accessed October 2020).
- Clifford S et al. Strategies to reduce the risk of SARS-CoV-2 re-introduction from international travellers. medRxiv. doi: 10.1101/2020.07.24.20161281.
- GOV.UK. Coronavirus (COVID-19): jobs that qualify for travel exemptions. www.gov.uk/government/publications/coronavirus-covid-19-travellers-exempt-from-uk-border-rules/coronavirus-covid-19-travellers-exempt-from-uk-border-rules (accessed October 2020).