Researchers explore prevention measures for SARS-CoV-2 transmission during international travel

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread like wildfire all over the world. A major contributing factor to SARS-CoV-2’s rapid and worldwide transmission has been international travel.

Travelers wear masks at Kuala Lumpur International Airport to prevent infection from coronavirus outbreak. February, 2020. Image Credit: Naufal Zaquan / Shutterstock
Travelers wear masks at Kuala Lumpur International Airport to prevent infection from coronavirus outbreak. February, 2020. Image Credit: Naufal Zaquan / Shutterstock

Over 60.24 million people across 191 countries and territories have been infected, and over 1.41 million have lost their lives. One of the key non-pharmacological interventions (NPIs) to curb any travel-related spread of SARS-CoV-2 has been restricting and monitoring international travel and movement.

Researchers from the Centres for Disease Prevention and Control (CDC) have released findings of their study titled, “Reducing travel-related SARS-CoV-2 transmission with layered mitigation measures: Symptom monitoring, quarantine, and testing,” on the preprint server medRxiv*.

Background

By March 2020, the spread of the infection across the globe was effectively mitigated by tight international travel restrictions. On March 11, the World Health Organization (WHO) declared the COVID-19 pandemic.

The transmission of SARS-CoV-2 has been steadily rising as international travel has slowly resumed over the past few months. This has occurred alongside other easements in lockdown restrictions in many parts of the world as governments were anxious to mitigate the major disruption that the virus has wrought on the global economy.

Travel and associated restrictions

Complete bans and restrictions of cross-border movements had a tremendous economic and individual impact, write the researchers. Slowly travel between nations started with checks in place.

These included personal measures as well as governmental measures.

  • Personal actions included:
    • wearing masks
    • social distancing at least 6 feet from others when possible
    • frequent handwashing or use of alcohol-based hand sanitizer
    • not touching one’s face
    • avoiding anyone who is sick or symptomatic
  • Measures by governments and airlines, airports and other businesses serving travelers included:
    • enhanced disinfection procedures
    • employee health assessments
    • passenger health attestations
    • screening for fever
    • illness response protocols
    • other steps to reduce the risk of transmission in airports and on conveyances

A three-step approach to preventing transmission

  1. Symptom screening

Symptom-based screening began at airports as international travel reopened. However, these measures were not very effective because measuring body temperature alone missed the mild, asymptomatic, and pre-symptomatic cases, which make up 20 to 40 percent of cases.

  1. Quarantine

The WHO defines quarantine as “the restriction of activities and/or separation from others of the suspect persons... who are not ill, in such a manner as to prevent the possible spread of infection.”

During a pandemic of this proportion, the WHO recommends a quarantine of 14 days based on the limit of the estimated incubation period for SARS-CoV-2. The authors of the study write, “A 14-day quarantine alone, when effectively implemented and strictly adhered to, approaches 100% reduction in risk of transmission post-exposure.”

  1. Testing

The third layer of protection against travel-related transmission includes rigorous SARS-CoV-2 testing. The researchers write that not all countries have implemented the mandatory testing of travelers before entry, but several countries are “requiring arriving travelers to be tested either prior to their departure or after arrival to identify infected persons who are asymptomatic so they can be isolated.”

Study design

Mathematical models can predict the effectiveness of symptom monitoring, testing, and quarantine measures to help prevent travel-related transmission of the infection. This considers several factors including, “infectious period, test-positivity relative to the time of infection, and test sensitivity.”

Findings

The researchers from their mathematical modeling estimates found the following:

  • Efficacy of isolation/quarantine and symptom monitoring
    • If the infection has occurred within days 0 to 7 days before the date of travel, isolation before travel or during travel can reduce the risk of transmission of the infection while traveling by 26 to 30 percent
    • Isolation based on symptom monitoring up to 7 days after travel with a positive infection reduces the risk of transmission by 42 to 56 percent
    • A 14-day quarantine after arrival, without symptom monitoring or testing, can reduce the risk of transmission by 97 to 100 percent
  • Testing before travel
    • If all travelers are tested before travel, the closer the test is to the date of travel, the lesser the risk of transmission is.
    • Testing on the day of departure can reduce risk while traveling by 37 to 61 percent.
  • Combined approach
    • A 7-day quarantine combined with symptom monitoring and testing on day 3 to 4 after arrival can reduce the risk of transmission by 95 to 99 percent
    • This method has the highest adherence
Reductions in transmission risk post-arrival assuming a 7-day exposure window prior to arrival and symptom monitoring, stratified by quarantine length, quarantine adherence, and day of test.
Reductions in transmission risk post-arrival assuming a 7-day exposure window prior to arrival and symptom monitoring, stratified by quarantine length, quarantine adherence, and day of test.

Conclusions and implications

The researchers concluded that the risk of introduction of the infection into a country due to international travel could be reduced by measures such as quarantine, an optimal test timing which is close to the time of arrival into the country. An effective quarantine should be imposed after arrival, along with testing a few days later. This can protect against the introduction of the infection into a country.

The team writes, “These measures can complement recommendations such as social distancing, using masks, and hand hygiene, to further reduce risk during and after travel.” They added in conclusion, “These findings can inform policies for travel until safe and effective vaccines become widely available.”

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.

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