Science

Timely travel restrictions helped countries keep Covid-19 rate low: Lancet Study

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Travel restrictions worked effectively for the countries that have a low number of Covid-19 cases but have a strong link with nations witnessing high rates of Covid-19 infection, says a study published in the journal Lancet Public Health.

The study stated that travel restrictions have been most effective when placed during the initial phase of the pandemic. The measures, however, did not show positive results when the virus was already spreading rapidly in a country.

Lead author Professor Mark Jit from the London School of Hygiene and Tropical Medicine, said: “We recognise that these measures carry high economic and social costs. So it is important that governments use travel restrictions in a targeted way.”

“Before introducing restrictions, they should take into account local infection figures, epidemic growth rates, and the volume of travellers arriving from countries heavily-affected by the virus,” Jit explained.

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For the study, the researchers analysed detailed flight data and compared the number of expected Covid-19 cases reported from international flights, with the number of infections arising from transmission within individual countries.

They produced estimates of international travellers in May and September 2020 based on the two scenarios.

One scenario used flight data for the same months in 2019, assuming no reduction in travel numbers, and the other scenario was based on the expected reduction in passenger numbers.

They estimated the numbers of Covid-19 cases using a mathematical model that adjusts recorded cases to take account of asymptomatic and unreported infections.

The study noted that where imported cases accounted for over 10 per cent of infections within individual countries, they were considered to have a major impact on the growth of the epidemic.

The work estimated that when imported cases accounted for less than 10 per cent, their impact on the growth of the epidemic was usually small, while those below 1 per cent would have an almost undetectable effect on the epidemic size.

The researchers said that had there been no travel restrictions in May 2020, the imported Covid-19 cases would account for more than 10 per cent of infections in the majority of countries included in the analysis.

Imported cases would account for no more than 10 per cent of infections in 34 out of 136 countries, and less than 1 per cent in four, they further said.

Speculations based on expected passenger numbers in May 2020, imported cases would have contributed to over 10 per cent of total incidence in 74 countries, less than 10 per cent of total incidence in 62 countries, and to less than 1 per cent in eight countries.

However, by September 2020, had there been no travel restrictions, imported cases would have accounted for over 10 per cent of infections in only a small number of countries.

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Imported cases account for less than 10 per cent of infections in 106 out of 162 countries, and less than 1 per cent in 21, the researchers said.

According to the estimates based on expected passenger numbers in September 2020, travel restrictions would have contributed to more than 10 per cent of infections in only 37 countries, less than 10 per cent in 125 countries, and less than 1 per cent in only 44 countries.

The researchers suggested that international travel restrictions were most effective at limiting local transmission of the virus during earlier stages of the pandemic.



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