Predicted Global Spread of SARS-CoV-2 Alpha Variant of Concern via Air Travel

PURPOSE: To predict the global spread of SARS-CoV-2 Alpha Variant of Concern (VoC) from England via air travel and compare against observed importation. METHODS & MATERIALS: Risk models were used to estimate a country's likelihood of importing at least one traveller infected with the Alpha VoC from England by January 19, 2021. First, the prior 60-day incidence of Alpha VoC associated with each English airport was estimated using cumulative Alpha VoC cases reported by Public Health England between September 20, 2020 – January 4, 2021 proportionately allocated to each airport. Each airport's catchment population was derived from a probabilistic Huff model. Next, the prevalence of the Alpha VoC for each airport was derived from the estimated incidence to represent the probability that at least one departing traveller was infected with the Alpha VoC for each English airport. The prevalence and forecasted flight volumes were used to estimate the likelihood of each destination airport receiving at least one infected traveller from England. Forecasted flight volumes were based on historical passenger volumes data from the International Air Transport Association and prospective flight schedules from CIRIUM. All airport-level likelihoods were aggregated to the country-level. Each country's predicted likelihood was compared against observed cases of Alpha VoC by January 25, 2021, collected by cov-lineages.org and a manual search of online sources. RESULTS: Among 211 countries, the median likelihood was 1.6% (interquartile range: 17.5%) and the mean was 13.9% (SD: 23.5%). In total, 28.9% (n=55) of countries had observed importation of the Alpha VoC by January 25(th). Fifteen of 16 countries with a predicted likelihood of importation greater than 50% had reported at least one case (kappa = 0.88), while 31 of 39 countries with a predicted likelihood lower than 1% did not detect a case (kappa = 0.92). CONCLUSION: Risk models based on air travel to inform public health preparedness accurately identified most potential destinations at highest risk of importing the SARS-CoV-2 Alpha VoC.