Air travel is currently on hold to check the spread of Covid-19, but a new study of 1,364 airports worldwide has found that if flights resume, cases could spread unevenly across the globe, with many of the airports in India and China posing the highest risk for the spread. The study says India’s population density and frequent domestic travel put it at high risk for outbreaks from infected passengers arriving from within the country.
The study estimates the risk for initiating an outbreak at various airports, after deriving these values from variables such as local population density and basic reproduction number. It estimates that the risk of initiating an outbreak in India is highest at Indira Gandhi International Airport in New Delhi at 0.5, followed by Chhatrapati Shivaji Airport at 0.45 and Kempegowda Airport in Bengaluru at 0.27; globally the airport with the highest risk to initiate an outbreak is Beijing Capital Airport at 0.74, followed by Hong Kong at 0.63 — Delhi is at fourth position globally, after Singapore at 0.53.
Contrary to the widely held belief that the threat of coronavirus spread from air travel comes from international travel, the study comes to the conclusion that the “highest risk to India is from domestic travellers”, i.e., the largest risk to initiate an outbreak arises from domestic flights, originating within India itself. Of the 10 highest-risk airports for India, eight are within the borders of India — the exceptions being airports in Dubai and Singapore. Among the 20 highest-risk airports, the study finds that 15 are located in India.
While the study covered airports globally, it specifically focused on Africa and India, both potentially vulnerable locations for spread of Covid-19. It complements the results of another recent study which showed that the spread of Covid-19 in Europe closely followed air travel patterns and that the severe travel restrictions implemented there resulted in substantial decreases in the disease’s spread. It emphasises that implementation of strict epidemiological control measures to prevent the spread of Covid-19 is likely not to be feasible or timely, and suggests that an additional layer of control measures, such as thorough screening of infected hosts, should be differentially implemented based on an airport’s risk to initiate a Covid-19 outbreak.
The study agrees that rapid, non-laboratory based methods of Covid-19 infection detection are still lacking, and screening relies on manifestation of symptoms (e.g. body temperature). Hence, individuals with asymptomatic or paucisymptomatic infections may still slip through even high coverage rates of screening at airports, until newer methods of screening are developed”.
The study, ‘Estimating COVID-19 outbreak risk through air travel’, has been conducted by two public-health and environmental-science experts from Tel Aviv University, who teamed up with a mathematician from the Oxford Mathematical Institute. It has not yet been certified by peer review. It produces a model of Covid-19’s spread using global air travel data for October — just before a second wave of COVID-19 might be expected — assuming a broad resumption of flights, accounting for global air-travel patterns and population densities, assuming viral spread is more likely when one infected traveller lands in a dense city than in a sparsely populated one.
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Importantly, the model in the study does not appear to account for current infection rates — the difference between Covid-19’s prevalence in New York and Kochi — but the study does drive home the point that reopening of air travel will have different effects in different cities.
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