Hong Kong’s third wave of Covid-19 cases could peak in two weeks, with sweeping social-distancing measures bringing the ratio of the number of people infected by each carrier down by more than two-thirds over the past fortnight, according to a leading expert.
Professor Gabriel Leung, dean of the faculty of medicine at the University of Hong Kong (HKU), said the fall in the “effective reproductive number” for the coronavirus meant the rate of an infected person spreading the pathogen to more than three others had fallen to just under one.
[Residents’ efforts] are to be commended, but [they] must be continued, and we must persevere for at least a few more weeks
Professor Gabriel Leung, dean of faculty of medicine, HKU
He also cited latest traffic data, which revealed that most age groups had reduced their mobility down to March levels when the health crisis last peaked, except students, some of whom might still be out and about during the summer holiday.
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“[Residents’ efforts] are to be commended, but [they] must be continued, and we must persevere for at least a few more weeks to suppress the epidemic dynamics,” said Leung, who is also a government adviser. “I am hopeful that the number of daily reported cases can peak in two weeks.
“We need to watch these indicators on a daily basis, and the moment they start to have an uptick or stop falling, then it’s probably time to quickly reassess whether we need more draconian measures,” he added, when asked about whether a lockdown might be necessary to flatten the curve.
The pandemic’s third wave in the city, which started more than a fortnight ago, has led to more than 800 infections, about 700 of which were locally transmitted and more than 300 others were without a known source. The city has recently logged beyond 100 new infections in daily caseloads.
On Thursday, the daily infection count hit a new record of 118, setting a high for the second day running, with the 15th patient dying.
The recent round of infections involved various clusters including elderly care home residents, hospital patients, as well as restaurant patrons and taxi drivers.
Leung warned on July 12 that the city’s Covid-19 reproductive number had shot up to between three and four people infected by a carrier, but he said on Thursday that the figure had plunged on the back of a raft of social-distancing measures, including school closures, two weeks ago.
The number fell to the current level of around 0.5 after more measures, including capping public gathering to groups of four, banning dine-in services at restaurants after 6pm and mandating mask-wearing on public transport, were put in place about a week ago.
The latest prediction was based on big data and artificial intelligence analysis of official case statistics and public transport volumes of Octopus card holders in the city, under a mathematical model known as “next generation matrix”.
The transport data showed the mobility levels of children, adults and the elderly had fallen back to March volumes that were at about 20, 50 and 50 per cent of pre-pandemic marks respectively in early January. These rose to about 80 to 90 per cent in June when social-distancing measures were relaxed and new daily cases eased.
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But the mobility levels of students, or those between the ages of 12 and 25, were still slightly above the March level of 30 per cent, Leung pointed out, as he urged young people to stay home.
Leung said given the positive data trends, he was hopeful the daily Covid-19 count could peak in two weeks, but cautioned that there was a reporting delay of three to seven days owing to the high volume of testing.
He warned that a “super-spreader event”, such as a cluster transmission in elderly care homes or hospitals, could not be predicted by mathematical modelling and could thwart the city’s efforts to control the crisis.
The infectious disease expert also revealed another research finding that showed differences in the genetic sequence of some third wave cases, meaning they were most likely not residual transmissions from the city’s second wave of infections in March.
Leung said the “working hypothesis” or credible explanation was that the latest cases came from multiple imported infections in those previously exempted from quarantine and testing, such as sea and air crew members.
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