Make sure you are up to date with your COVID-19 vaccines before you travel abroad. Getting vaccinated is still the best way to protect yourself from serious illness and slow the spread of COVID-19.People who are not up to date with their COVID-19 vaccines should follow additional recommendations after travel. Based on evidence at the time, WHO did not recommend any travel restrictions when it declared that COVID-19 was a public health emergency of international concern (ESPII). The study investigated domestic and international travel measures, including a wide range of travel measures.
The study concludes that domestic travel measures implemented in Wuhan were effective in reducing the import of cases internationally and within China, and were likely to be important additional travel restrictions as well. The study also reveals that travel measures are most effective when implemented early in the outbreak. The findings highlight the need to assess the potential effectiveness of travel measures through an assessment based on the risk and context of each specific outbreak and the types of measures used. The findings of this study also suggest the need to strengthen the ESPII process in such a way as to increase the likelihood that travel measures, when justified, can be implemented quickly enough to maximize their effectiveness.
The near-universal adoption of travel-related measures, especially in the light of potential significant economic and social consequences, raises questions as to whether such measures can and have been effective in reducing international transmission of the virus during the pandemic. Previous infectious disease outbreak studies have suggested that certain travel-related measures have only limited or, at best, modest effectiveness in containing influenza outbreaks. For example, a systematic review of the effectiveness of international travel measures (screening, travel restrictions and border closures) in controlling pandemic influenza identified 15 studies and found that measures implemented in a timely manner could delay local transmission by a few days or weeks, curb international spread. and delaying the epidemic peak in isolated locations by reducing the number of seeding events 9.The review did not identify any evidence that screening methods were effective, but did find that border closures had been effective in preventing the introduction of the virus into small island states during the 1918 influenza pandemic.
However, the authors also concluded that the general evidence base on which they drew their conclusions was small and of poor quality. A related but broader review of a wider range of measures, including travel advice, examinations, internal travel restrictions and border closures, for both epidemic and pandemic influenza, also found that travel restrictions could delay the arrival and spread of epidemics and that they are selected secluded places. can benefit more from border closures. However, once again, the overall effect sizes were relatively small and the quality of evidence was also very low.
10.Another review of domestic and international travel restrictions concluded that such measures could delay, but not contain, the spread of pandemic and seasonal influenza. 11.Based on the 23 studies identified, the review concluded that domestic and international border restrictions could delay the spread of an outbreak by 1 week and 2 months, respectively, and that such restrictions could delay the spread and peak of epidemics from a few days to up to 4 months. However, the timing of such measures was key; the extent of delayed spread was significantly reduced when restrictions were imposed more than 6 weeks after the onset of an epidemic. Beyond influenza, evidence of other infectious disease outbreaks is more limited.
A modeling study of travel restrictions implemented during the Ebola outbreak in West Africa estimated that these measures could have delayed international transmission by some weeks in some countries.12 Given the low proportion of international travelers from Ebola-affected countries at the time, another study suggested that exit detection measures in affected countries would likely be more effective in reducing further international transmission than travel restrictions13, a finding that was supported by a similar study14 The WHO travel advisories issued during SARS 2003, which caused a substantial decrease in international travel to Hong Kong and mainland China, was estimated to have delayed the export of cases by only a few days. Importantly, other studies have suggested that travel measures during outbreaks may be counterproductive by preventing countries from launching effective epidemic responses16, undermining case detection and causing widespread economic effects on the travel industry itself.17 To carry out this review, we adopted an abridged version of the Protocol of Preferred Reporting Elements for Systematic Review and Meta-analysis (PRISMA) using the 17- 23 The rationale for the study was the widespread adoption of travel measures, despite the consensus view at the time that such measures were largely ineffective and to strengthen the implementation of the IHR during this and future pandemics. The objectives were to rapidly review the evidence of the effectiveness of the full range of travel measures taken during the first phase of the COVID-19 pandemic, both from published and unpublished studies. Below, we detail other methods of the study.
Given the rapidly evolving nature of the outbreak, as well as the rapid expansion of published literature on COVID-19, our search strategy focused on both pre-printed and published articles, and strategies for identifying each of them differ slightly. Keywords were identified both on the basis of inductive iterative testing of possible keywords, and deductively through documents identified through other channels. Search terms were refined to minimize overlap and maximize the number of studies that could be identified. While we don't impose a language restriction, we don't specifically look at sources that aren't in English.
After the screening, we were left with 79 articles. The full texts of each one were obtained and they were re-uploaded to Covidence. Two reviewers re-examined each article to determine whether the article still met the inclusion criteria. Any disagreement between the two reviewers was again reviewed by a third reviewer (KG) who did not otherwise participate in the selection process.
After the evaluation of the full text, we were left with 30 studies that met all of our selection criteria. Of these, one study investigated socioeconomic outcomes, which we excluded from this analysis given the lack of overlap in the results. Effect of international travel measures Effect of the application of interprovincial travel measures The results included the number of cases observed, the date of the epidemic peak, the risk of transmission, the rate of growth of cases, the doubling time, the time of arrival in a new country, the reproductive number (R0 or Rt ) and cumulative cases. The details are listed in tables 2 and 3, which summarize the documents investigating domestic and international travel measures, respectively.
In both tables there is an article that evaluated the effectiveness of both types of measures28. Beyond the direct effect of the Wuhan travel ban, Chinazzi et al28 estimated that the application of additional travel restrictions, in this case, the reduction of flights between mainland China and receiving countries, led to substantial additional reductions in cases imported globally, although the degree of reduction varied by country and the extent of flight reductions. Namely, reductions in international traffic of 40 to 90 per cent between China and other countries could have led to large additional declines in imported cases and significant delays in the arrival of a substantial number of cases to other countries until early March. Adiga et al34 investigated the impact of travel measures imposed by the government or airlines against China and estimated that this resulted in a delay in the import of the virus of about 4-5 days on average and up to 10 days in some countries.
However, this study did not directly control the impact of the Wuhan closure, which occurred more or less at the same time as many of the measures investigated. In terms of country-specific case studies, Adekunle et al35 found that Australia's ban on air travel to and from China may have prevented 82% of imported cases as of February 2. Anzai et al31, who focused on the impact of the ban on the outbreak in Japan, estimated that the absolute risk of a major outbreak was only moderately delayed due to the travel ban to Wuhan and that the average delay in a major outbreak was only 1 to 2 days. Similarly, Costantino et al36 estimated that it could have led to a 79% reduction in imported cases up to March 2.
Linka et al37 estimated that travel restrictions implemented on both the external and internal borders of the European Union significantly slowed the spread of the virus in member states, especially in Central European countries. These last two studies, both focused on an earlier period of the pandemic, did not take into account the impact of the Wuhan closure, in addition to the restrictions evaluated. Studies investigating the effectiveness of screening found that only highly effective screening could reduce (or decrease) the risk of import or export. Clifford et al38 found that when the number of cases was low in the exporting country, screening could delay the onset of the epidemic in the importing country by up to a week, while Mandal et al39 found that if screening could detect 90% of asymptomatic people, it could delay the average time of the disease.
epidemic. up to 20 days in selected countries. Assuming that self-identification of cases was effective, another study suggested that such measures could identify a large proportion of infected travelers. However, this means that screening tests are effective, but they do not study it directly.
32 A single observational study identified in this review investigated the impact of border restrictions, in combination with mandatory quarantine and screening, on travelers arriving in Hong Kong. Cowling et al30 concluded that the implementation of quarantine measures on travelers arriving in the region was an important element of their successful public health response, but the study does not specifically estimate its impact independently of other measures, including travel-related measures. In Table 3, we present the findings of studies that investigated the impact of travel restrictions to Wuhan on domestic export of cases to other parts of China. Comparing the actual cases observed with counterfactual scenarios in which such measures had not been imposed, Chinazzi et al28 predicted that the travel ban led to a 10% reduction in cases exported within the first 7 days, Fang et al40 estimated a reduction of 39.3% for 1 month.
Shi, Fang41 similarly identified a 39% reduction in cases over 1 month, while Tian et al42 estimated a 73% reduction through mid-February. Tang et al43 found that the travel ban to Wuhan led to a 91.1% reduction in imported cases into Beijing for more than 7 days. Similarly, Kraemer et al44 also found that these travel measures drastically reduced outbreak transmission across the country, with areas that had greater pre-lockdown connectivity with Wuhan experiencing a greater decline. Aleta et al45 considered that the measures were effective in reducing the export of cases, but only in the short term.
Yuan also found that the blockade is effective in reducing the number of cases outside Wuhan, but notes that the timing also coincided with a national stay-at-home campaign imposed by the Chinese central government. 46 The studies also investigated the impact of the travel ban at the national time of the outbreak. Tian et al42 estimated that the ban delayed outbreaks within China by 2.91 days, while Chinazzi et al28 estimated a delay of 3 to 5 days. The studies also investigated the impact of the travel ban on the effective reproductive rate, doubling time and other measures.
Hou et al47 found that the ban quickly reduced the reproduction rate of the virus outside Wuhan; similarly, Li et al48 found that the number of breeding stock fell by more than half within 2 weeks after the ban was introduced. Using observational data, Lau et al49 found that the doubling time of the virus increased from 2 days to 4 days after the imposition of the travel ban. Another study found substantial decreases in transmission routes between Chinese provinces within weeks of the introduction of travel bans to Hubei. 50.
The timing of travel-related measures, once again, appears to be important in predicting effectiveness. Both Lai et al and Liu et al., the first, a model-based study and the second, an observational study, estimated that the travel ban to Wuhan would have been substantially more effective if it had been implemented 1-3 weeks earlier, 51 52 This is supported by Wu et al53, who found that the travel ban had a relatively minor effect on the overall speed of transmission of the outbreak in areas of China outside Wuhan, largely because a large number of cases had already been exported before the travel ban, limiting its effectiveness. Finally, some studies evaluated domestic travel bans in combination with other travel-related measures. For example, a model-based study estimated that if China's major cities had imposed additional measures, they could have further reduced their risk of an epidemic.
Despite the lack of WHO recommendations on travel measures and given the evidence of the limited effectiveness of such measures in other contexts at the start of the COVID-19 pandemic, there was an unprecedented adoption of such measures during the first phase of the pandemic, both nationally and internationally, which contributed to a drastic decline in international travel. This document reviewed emerging evidence on the effectiveness of travel measures taken during the first phase of the COVID-19 pandemic and identified several key findings. First, there was a high level of agreement among the reviewed studies that the adoption of travel measures played an important role in shaping the early transmission dynamics of the COVID-19 pandemic. Internationally, studies consistently estimated that travel measures to Wuhan led to a 70-80% reduction in exported cases in the first few weeks, and probably had a minor effect in mainland China, where effectiveness estimates ranged from 10 to 70%.
In addition, the travel ban to Wuhan likely caused delays of up to a few weeks in the importation of cases to other countries. The additional travel measures, namely the reduction in the number of flights to countries, had an additional effect on reducing the number of imported cases. However, almost all of the studies in this review focused on domestic or international travel bans imposed on Wuhan and, to a lesser extent, on the rest of China, during the initial period of the pandemic. As such, this review does not identify substantial new evidence of the effectiveness of travel-related measures aimed at controlling the spread to and from other parts of the world or beyond the initial export of cases outside China.
Second, most studies also agreed that the effect of the Wuhan specific measures was short-lived, partly because, over time, other provinces became the source of most cases exported internationally from China. This suggests that specific measures related to travel against specific countries alone may not be sufficient, since knowledge about where a new virus circulates may be limited from the outset and that countries should also start implementing national public health containment measures together with international travel measures. This view is supported by evidence identified in this review that suggests that once four or more infections are introduced in a new location, there is more than 50% chance of a major outbreak (in the absence of other interventions). Several studies supported the view that within China, if the same policies had been implemented a few weeks earlier, there would likely have been substantially less spread of the virus across the country and internationally.
In fact, as noted above, some jurisdictions (such as Taiwan, Russia and Macau) acted faster than Wuhan in implementing travel measures. While the Wuhan measures may have been too slow to be optimally effective, they were implemented a week before WHO issued the ESPII declaration. Fifth, during the initial phase of the pandemic, there are likely to be a large number of undetected cases worldwide and, although some studies allowed their estimates to vary depending on the assumed proportions of undetected cases, the validity of the estimated effects in all of these studies is likely to be seen affected by data quality problems. In addition, since symptomatic individuals may be more likely to slow down their travel than asymptomatic travellers, especially internationally, and after the introduction of travel-related measures aimed at detecting symptomatic cases, modeled efficacy studies may be biased if they do not have tell this difference.
In addition, some of the measures taken related to travel (e.g. screening) may have led to increased case detection48, which could further complicate the evaluation of the effectiveness of travel measures, since the measurement of outcome was also influenced by intervention and few studies recognized this limitation. Finally, although this study identified a relatively large number of studies, we assessed that the quality of these studies is generally low. Almost all of the studies identified in this review were modeled studies and, therefore, the results depend on assumptions of important parameters that varied considerably.
Given the dynamic and rapidly evolving nature of the pandemic, it is unclear how close these assumptions were to reality. Comparability between studies is also undermined by a lack of standardized terminology. In addition, few studies attempted to isolate the potential effect of international travel-related measures from a series of concurrently implemented national measures, or from other social, political or economic characteristics of the application or destination locations or populations. This systematic review also has several important limitations.
First, while our goal was to be systematic in our search strategy, as well as inclusion criteria, the rapid expansion of the literature on the COVID-19 pandemic almost certainly means that we probably missed some relevant studies. Secondly, while our goal was to focus on the initial phase of the outbreak, it is not clear when was the right time to finish our review. The most recent studies that have been published since we completed our bibliographic search may present a different picture of the effectiveness of travel measures and, therefore, the evidence of this study should be evaluated in this context. Third, assessments of bias in studies are challenging and inherently subjective.
While WHO did not initially recommend such measures, it has over time softened its stance on such measures. In May, the IHR Emergency Committee had recommended that WHO update its recommendations to include measures that would be better to “balance the benefits of such measures with their unintended consequences”. The universal use of travel-related measures by States parties during the COVID-19 pandemic will likely be an important topic of discussion on the limitations of the current treaty. Based on this review, we draw the following conclusions to inform those discussing ways to better integrate evidence into the IHR process and to inform better responses to future outbreaks.
First, the findings of this review suggest that it is very difficult to know, in the early stages of an outbreak of a new infectious disease, the effectiveness of travel measures. Therefore, evaluations of the potential effectiveness of such measures cannot be inferred from previous outbreaks of infectious diseases, especially when the clinical and epidemiological characteristics of the virus are unknown. It also stresses the need to move from general assessments of the effectiveness of travel-related measures (“travel measures do not work”) to recognize that pathogen-specific assessments of effectiveness based on possible transmission risk scenarios (“for which types of threats”) could such measures be effective? '). Due to the limited transparency of the ESPII declaration process, it is unknown which risk assessments were carried out by the Emergency Committee or how.
As both the level and range of measures taken by countries during COVID-19 were very different from previous ESPII, future assessments should consider a full range of possible scenarios. Secondly, it is also clear that the effectiveness of travel measures cannot be estimated using a single fixed parameter. The effectiveness of the measures will vary depending on the environment, what other measures are also implemented (nationally and internationally), the extent to which they are implemented and the speed with which they are implemented. All these factors, compared to potential harm, should also be taken into account in discussions on the possible effectiveness of international travel measures.
Therefore, decision-makers should further consider context-specific assessments of the effectiveness of such measures (“when and where could such a measure be effective?”). Third, this study finds that measures implemented early were likely to be more effective than those implemented late. In this pandemic, the ESPII declaration was not made until after many countries had begun to adopt travel measures, and when it was, WHO recommended that such measures not be taken. In addition, the IHR requires States Parties to provide evidence of any additional health measures they implement.
In the context of an outbreak of a novel infectious pathogen, it is not clear what constitutes evidence in the early stages of the outbreak. The importance of evidence, especially when such evidence is unlikely to exist, must be balanced against the potential for risk and the need to implement containment measures early. At the beginning of the COVID-19 pandemic, there was a widespread belief that travel measures were unlikely to play a significant role in containing the international spread of the virus. However, the widespread adoption and persistent use of such measures, worldwide, as well as the evidence identified in this review, challenge this belief in favor of a more nuanced view.
While this review emphasizes that the quality of evidence remains low and highlights many methodological deficiencies in the reviewed studies, the findings also identified new evidence of the impact of such measures during the initial phase of the pandemic. These findings suggest that travel measures did play an important role in shaping the initial dynamics of the pandemic, even if they could not contain the virus globally on their own. Along with many other transformations catalyzed by COVID-19, the pandemic has also challenged our views on what constitutes evidence of the effectiveness of international travel measures 57.This web-only file has been produced by BMJ Publishing Group from an electronic file provided by the author (s) and has not been edited for the content. Collaborators KG developed the study methodology, wrote the manuscript and supervised the analysis of the data.
ZL and T-LH conducted systematic review search, article selection, data extraction and data analysis. KL, CZW, SM and JP contributed to the study design and contributed to the manuscript. Patient consent is not required for publication. Provenance and peer review Non-commissioned; externally reviewed.
Data Availability Statement All data relevant to the study are included in the article or uploaded as supplementary information. Given the widespread adoption of travel restrictions and the likely enormous economic and social consequences resulting from them, a fuller understanding of the effectiveness of all measures taken during the first phase of the pandemic is warranted. Articles that were news reports, review articles, commentaries or editorials, or conjectures (i.e. did not provide new data or evidence) on the effectiveness of travel measures were excluded.
We used the same travel-related keywords to search the WHO global COVID-19 research database, but we did not impose a search term for COVID-19, since, in theory, all articles in this database. That review identified 36 studies, of which 25 were specific to COVID-19 and concluded that cross-border travel measures can limit the spread of the disease across national borders, specifically in terms of reducing the number of imported cases and delaying or reducing the development of the epidemic, although it is found that the certainty of the reviewed evidence was low to very low. Although this was a national policy and therefore outside the scope of the IHR, this review suggests that restricting travel to and from Wuhan dramatically changed the output of cases from the region in a crucial period.