Travel measures in the SARS-CoV-2 variant era need clear objectives
Such strategies—eg, vaccine passports, reactive flight bans, isolation of travellers who test positive for SARS-CoV-2 or blanket quarantines, and major changes to travel protocols—have often had weak accompanying justifications. Many governments continue to adapt various combinations of international travel measures and, increasingly, scale them back (figure) without stating clear objectives or the evidence behind them. In an era of SARS-CoV-2 variants and for future pandemic preparedness, there is a need for a transparent and evidence-based approach to travel strategies, supported by the development of clear international standards.
FigureChanges in proportion of countries with particular stringency of travel control measures over time
and could provide governments time to develop long-term strategies, such as reinforcing surveillance, contact tracing, public health measures, and vaccination campaigns. However, the marginal value of delaying importation of variants such as omicron (B.1.1.529) has declined in many countries because the speed of importations far exceeded the ability of most governments to implement reactive travel policies. Once variants are established locally, ongoing travel restrictions will have extremely limited impact on the local epidemic.
Furthermore, imposing travel restrictions on countries that discover and report new variants could be a disincentive to rapidly reporting findings, damaging a vital early warning system for the rest of the world.
stringent domestic restrictions were required to contain subsequent outbreaks in the pre-vaccine era, and containment has become harder with more transmissible variants. Stringent quarantine for all travellers also comes with substantial individual and societal costs. However, such costs may be mitigated through the use of testing after arrival, with test-to-release schemes decreasing the time required for quarantine.
Modelling studies have estimated that repeat rapid antigen tests are more likely to detect active infection than less frequent PCR tests, which are often associated with slower results and higher costs.
Daily testing of individuals considered a potential transmission risk with rapid antigen tests might also feasibly replace home quarantine with no expected increase in onwards transmission.
Another potential approach might include trained dogs that distinguish between infected and uninfected individuals using odour samples.
,
An advantage of this approach would be its speed and the fact that a laboratory specimen or test kit is not required; dogs can potentially screen up to 250 travellers per hour per dog, and trials are underway in the UK.
However, more evidence is needed before such an approach could be routinely implemented.
then proof of vaccination alone would not be sufficient to prevent the importation of such variants, as shown by the spread of omicron. Certification can therefore only be one component of a wider risk mitigation strategy. Moreover, fake vaccination certificates and test results are being identified in many countries,
and as more countries redefine fully vaccinated to include boosters and introduce domestic vaccine passport policies, ensuring alignment of standards internationally will become increasingly important.
However, use of reported cases as a measure of equivalency is fraught with difficulty: routine case data do not account for the limited reporting capacity in many countries or variation in actual testing strategy from country to country. Given the extensive SARS-CoV-2 testing for travel that is being used globally, it is a missed opportunity that test data have not been better used to improve understanding of global SARS-CoV-2 dynamics. Testing at arrival not only provides information about incoming infections, it also enables estimation of prevalence in countries of departure. Routine sharing of such data could inform risk assessments for any future measures based on equivalent epidemiology.
negotiated by WHO member states, could serve as a clearing house for evidence obtained from various government strategies, and help coordinate actions by governments to decrease variant risk and disruption to international travel.
JGL is an academic at the London School of Hygiene & Tropical Medicine (LSHTM) and the Chief Executive Officer of Arctech Innovation, a spin out company from LSHTM; the company is working on the development of sensors for the detection of
diseases including COVID-19. AJK is supported by the Wellcome Trust (206250/Z/17/Z). SC is funded by the Wellcome Trust (208812/Z/17/Z) and UK Medical Research Council (MC_PC_19065). MC is funded by the Wellcome Trust (220977/Z/20/Z). All the other authors declare no competing interests.
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Published: March 02, 2022
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