London, March 26 : In order to fight a pandemic, travel restrictions are most useful in its early and late phases, a new study suggests.
Analysis of human mobility and epidemiological data by a global consortium of researchers, led by the University of Oxford in the UK and Northeastern University in the US, shows that human mobility was predictive of the spread of the epidemic in China.
"Our findings show that early in the coronavirus outbreak travel restrictions were effective in preventing the import of infections from a known source," said study researcher Moritz Kraemer from the University of Oxford.
Restrictions of travel from Wuhan province in China, unfortunately, came too late.
The research, published in the journal Science, showed that the impact of travel restrictions declines as the epidemic grows.
Provinces outside Hubei that acted early to test, track and contain imported coronavirus cases fared the best in preventing or containing local outbreaks, the study said.
Mobile geolocation data from China-based search engine giant Baidu Inc, combined with a rich epidemiological dataset from the Open COVID-19 Data Working Group, showed that local person-to-person transmission happened extensively early on in the coronavirus outbreak and was mitigated by drastic control measures.
However, with an average incubation period of five days, and up to 14 days in some cases, these mobility restrictions did not begin to positively impact the data on new cases for over a week -- with things appearing to get worse in the 5-7 days immediately after the lockdown as local transmission was well under way.
According to the researchers, among the cases reported outside Hubei, 515 had a known travel history to Wuhan and a symptom onset date before January 31, 2020, compared with only 39 after this date, illustrating the effect of travel restrictions in decreasing the spread to other Chinese provinces.
"This is where a full package of measures, including local mobility restrictions, testing, tracing and isolation need to work together to mitigate the epidemic," Kraemer added.
Chinese provinces and other countries that have successfully halted internal transmission of COVID-19 need to consider carefully how they will manage to reinstate travel and mobility to avoid the reintroduction and spread of the disease in their populations, the researchers said.
"Travel and mobility restrictions are the most useful right at the start, when local transmission has not yet become a factor," said Samuel V Scarpino, Professor at Northeastern University.
"After transmission is established, physical distancing and the quarantine of sick individuals will work, but it takes time," Scarpino added.