Addendum needed on COVID-19 travel study


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.

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