Addendum needed on COVID-19 travel study
Authors: Lee Altenberg
Journal: The Lancet Infectious Diseases (2021)

The Article by Mathew Kiang and colleagues1Kiang MV Chin ET Huynh BQ et al.Routine asymptomatic testing strategies for airline travel during the COVID-19 pandemic: a simulation study.Lancet Infect Dis. 2021; 21: 929-938Summary Full Text Full Text PDF PubMed Scopus (36) Google Scholar is one of very few studies available to inform policy makers in Hawaii, USA, on the efficacy of different testing and quarantine strategies for preventing new introductions of SARS-CoV-2 variants into the island populations. The primary endpoint of the study—the cumulative number of infectious days—is proposed to measure the risk to the destination population of importing infection through travel. However, the tallies include infectious days before travel, which do not expose the destination population. To assess exposure to the destination population only, the tally should start on the day of travel. Such a tally is shown in figure A, which overlays graphs from figure 1 of Kiang and colleagues' Article. Aligned are the curves for no testing and strategy 1 (PCR test within 3 days of departure) so as to start the count of infectious days on the day of travel. By this measure, the 3-day pre-travel test reduces the days of exposure to the destination population by only 20% relative to no testing, less than the reported 36% reduction that includes pre-travel exposure days. Another confusion comes from the tally of infectious days during the 5-day post-arrival quarantine simulations. In figure B, the curve for strategy 1 in the study by Kiang and colleagues is overlayed with the curve for strategy 2 (PCR test within 3 days of departure and PCR test on day 5 after arrival, with 5 days of quarantine upon arrival). It shows that quarantine has no effect on the cumulative days of exposure until day 5 and beyond. For some reason, Kiang and colleagues included the travellers' infectious days during 5 days of quarantine in the cumulative count, even though these days are not exposing the destination population. If the infectious days during the 5-day quarantine period were excluded, the reduction in exposure to the destination population under strategy 2 would be far greater than the 70% reported in the study. Finally, most helpful would be to add a table that shows, for each strategy, the number of infectious people on each day of travel. I report, outside this work, grants from the Foundational Questions Institute, personal fees from Trials.ai, and grants and non-financial support from the Stanford Center for Computational, Evolutionary and Human Genomics and the Morrison Institute for Population and Resources Studies, Stanford University. Addendum needed on COVID-19 travel study – Authors' replyWe thank Lee Altenberg and Mohammad Shahid for their comments on our study.1–3 Despite efficacious COVID-19 vaccines becoming available since our study was originally designed, the use of routine testing for SARS-CoV-2 during travel has become increasingly relevant due to: (1) groups of people who have declined vaccination, (2) vaccine-breakthrough infections (that might be symptomatic or asymptomatic), (3) new variants with higher degrees of infectiousness, and (4) lack of access to vaccination in many parts of the world. Full-Text PDF Routine asymptomatic testing strategies for airline travel during the COVID-19 pandemic: a simulation studyRoutine asymptomatic testing for SARS-CoV-2 before travel can be an effective strategy to reduce passenger risk of infection during travel, although abbreviated quarantine with post-travel testing is probably needed to reduce population-level transmission due to importation of infection when travelling from a high to low incidence setting. Full-Text PDF