- SARS-CoV-2 Infection Risk Imposed by Fully-vaccinated Air Travelers Attending an Island-confined Quarantine System Enabling Tourism During the Pandemic: A Retrospective Cohort Study
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Thunyaporn Sirijantradilok, Chanapong Rojanaworarit, Isabella Andrade, Worawaran Kallayanasit, Panunda Yodkhunnathum, Somruethai Khamsakhon, Supasit Suerungruang, Nuttawoot Photisan
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J Prev Med Public Health. 2024;57(6):552-563. Published online September 23, 2024
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DOI: https://doi.org/10.3961/jpmph.24.351
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 Abstract
Summary
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- Objectives
This study aimed to identify the incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among fully vaccinated air travelers participating in an island-confined quarantine system (Phuket Sandbox Program). It also compared the differential risk of SARS-CoV-2 infection across different coronavirus disease 2019 (COVID-19) vaccines and the difference in time-to-detection periods between asymptomatic and symptomatic cases.
Methods
This retrospective cohort study determined the cumulative incidence of SARS-CoV-2 infection among 63 052 air travelers who participated in a quarantine program from July 1, 2021 to October 31, 2021. Using Poisson regression with robust standard errors, we estimated the relative risk of SARS-CoV-2 infection across different brands and types of COVID-19 vaccines, adjusting for relevant covariates. We visualized the time-to-detection periods for SARS-CoV-2 infection using Kaplan-Meier failure curves and compared these curves for asymptomatic and symptomatic travelers using the log-rank test.
Results
The overall incidence of SARS-CoV-2 infection was 0.3%. Individuals vaccinated with Ad26.COV2.S, Gam-COVID-Vac, CoronaVac, and replicating viral vector vaccines faced a significantly higher risk of infection than those who received the BNT162b2 and mRNA vaccines. The time-to-detection periods for asymptomatic and symptomatic cases did not differ significantly.
Conclusions
Despite the relatively low risk of SARS-CoV-2 infection, a risk of breakthrough cases remained with certain vaccines. Given the high proportion of asymptomatic cases, quarantine and intermittent testing should be implemented. The mandatory quarantine system proved effective in managing positive cases without necessitating a complete shutdown of travel. Implementing an island quarantine could be a viable strategy for reintroducing travel and tourism during a future COVID-19 outbreak or a new pandemic.
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Summary
Key Message
"This study evaluated the SARS-CoV-2 infection rate among 63,052 fully-vaccinated air travelers participating in the Phuket Sandbox Program in 2021. A breakthrough SARS-CoV-2 infection rate of 0.3% was identified. Travelers vaccinated with Ad26.COV2.S, Gam-COVID-Vac, CoronaVac, and replicating viral vector vaccines exhibited a higher risk of breakthrough infections than those vaccinated with BNT162b2 or other mRNA vaccines. The island-confined quarantine system combined with confirmatory COVID-19 testing effectively identified post-arrival infected travelers, demonstrating its potential as a model enabling safe tourism while preventing importation of cases into communities beyond the island during the pandemic."
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