Two new studies suggest the importance of using a suite of containment measures to stop the spread of COVID-19, ranging from border control to school closures.
The first, published in the journal Proceedings of the National Academy of Sciences, found that border control measures enacted in China to contain COVID-19 likely slowed the rate of infection outside of the mainland, but are insufficient to contain its global spread.
In the early stages of the outbreak, China implemented travel lockdowns in Wuhan, the city where it originated, as well as other cities in the Hubei province. Since then, other countries have followed suit, implementing airport screenings, restrictions on travel and mandatory self-isolation periods for travellers.
A team of researchers from a range of organisations including the Center for Infectious Disease Modelling and Analysis at the Yale School of Public Health, US, estimate that without travel restrictions, 779 cases of COVID-19 would have been exported by February 15, 2020.
The Chinese lockdowns reduced this number by more than 70% and the estimated daily exportation rate by more than 80% during the first three and a half weeks of implementation.
“Our results demonstrate that travel restrictions cannot be expected to fully arrest the global expansion of COVID-19 but may decrease the rate of case exportations if enacted during the early stages of the epidemic,” write lead author Chad Wells and co-authors.
The researchers also highlight that nearly two-thirds of exported cases were estimated to be pre-symptomatic upon their arrival which meant airport screening measures had limited effectiveness.
“We find that airport screening has only a moderate benefit during the early stages of the epidemic, as about 64% of infected individuals travel during the incubation period and exhibit symptoms an average of three days after arrival,” they write.
Another study published on the pre-print site medrxiv, found that the time between cases in a chain of transmissions was less than a week, with more than 10% of patients being infected by someone who has the virus but does not yet have the symptoms.
“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide,” says researcher Lauren Ancel Meyers from The University of Texas in Austin, US.
“This tells us that COVID-19 outbreaks can be elusive and require extreme measures.”
Both studies confirm that additional containment measures such as rapid contact tracing within an epicentre and self-isolation could be important in limiting the global spread of the disease.
“This study provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” says Meyers.
“Asymptomatic transmission definitely makes containment more difficult.”