A fourth wave of Covid-19 infections is looming in Hong Kong, experts say. In the first of a three-part series, the Post looks at when and why a spike in infections is expected and how the flu season can get in the way of containing the coronavirus.
Hong Kong is on the brink of a fourth wave of Covid-19 infections because of a combination of factors, from untraceable cases in the community, to sick travellers slipping past checks, and the looming flu season, health experts warn.
They worry that as Hong Kong eases pandemic travel restrictions and allows more visitors, undetected imported infections will set off another spike in cases especially if they combine with untraceable ones in the city.
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Experts are in favour of a massive flu vaccination campaign this year, because dealing with a surge in Covid-19 infections could become complicated if winter brings a sharp increase in cases of flu.
“I am a bit worried that our fourth wave might start sooner than we were hoping,” said Professor Benjamin Cowling, head of epidemiology and biostatistics at the University of Hong Kong’s school of public health.
Hong Kong has already been hit by three waves of the coronavirus since early this year. More than 120 people were infected in the first round, which began in January, and over 640 people in the second, which started in March. There were seven deaths in those two waves.
The third wave came in early July, when infections spiked. The total number of cases has swollen five-fold from just over 1,000 in early July to 5,113 as of Sunday.
Infections swept through the city, affecting care homes for the elderly and disabled, public hospitals, detention facilities, wet markets and a container terminal.
The city’s Covid-19 death toll also rose sharply to 105 as of last Friday, with elderly people accounting for most of the dead.
When we have infections locally and we are not doing much social distancing, numbers will tend to go up from week to week
Professor Benjamin Cowling
The city has relaxed social-distancing measures, including doubling the maximum number of people who can gather in public to four, and reopening venues such as beauty salons and gyms.
But experts are concerned that the source of infection has been untraceable for close to one in three local cases during the past two weeks.
They include a 71-year-old resident at Yuen Long Home for the Elderly, a nurse at Queen Elizabeth Hospital, and a traveller from Thailand who has stayed at four different hotels since March.
Professor Cowling warned it would take only a few local transmissions in the community to spark a fourth wave.
“What we have learned from the last nine months of Covid-19 is that when we have infections locally and we are not doing much social distancing, numbers will tend to go up from week to week,” he said.
So, he is worried that with the recent easing of restrictions, allowing the reopening of venues such as bars, cinemas and karaoke lounges, the next spike in infections could happen anytime now.
Agreeing, two government coronavirus advisers were also concerned that a much touted plan to create “travel bubbles” and reopen the border would result in importing the virus once again.
David Hui Shu-cheong, a professor of respiratory medicine at Chinese University, believed the fourth wave would be triggered by imported cases just as in the earlier spikes.
Research has shown that imported cases played a key role in spreading the virus in the community in the first three waves of the infections – the first was triggered mainly by a pair of tourists arriving from the mainland, the second by students and working people returning from Europe and North America, and the third by sea and aircrew who were exempted from quarantine.
“One needs to be careful when the border is reopened,” Hui said.
Professor Gabriel Leung, dean of HKU’s faculty of medicine, said community outbreaks had been curbed largely because there were only a few remaining chains of transmission locally, and they had not come together to initiate a new wave of infections.
“If there are more imported cases that slip through the net, and the local transmission chains begin to coalesce, the scale of the outbreak can be very large indeed,” he said.
Leung, who tracks Hongkongers’ travel habits through Octopus travel card data, found it worrying that people had resumed moving about at pre-pandemic levels.
At the height of the third wave of infections, in July, travel dropped to a fifth of what it was in January, before Covid-19 arrived.
Leung is also keeping an eye on the reproductive rate of the virus, which refers to the number of people scientists believe each Covid-19 patient is able to infect.
In April, when social-distancing measures were in full force, the rate dropped sharply to a low of 0.1. At the peak of the third wave in July, it shot past three.
Leung is concerned that although third-wave infections have come down, the reproductive rate has hovered between 0.45 and 0.6 for the past six weeks, which indicates that the virus is still in the community and there are infected people who have not been traced.
Leung flagged the reopening of borders as another area to watch.
The authorities have said a health code system has been prepared to allow Hongkongers living on the mainland to come to the city to visit their families, once they obtain a negative Covid-19 test result.
Senior officials have also revealed they are in talks with 11 countries, including Japan, France and Germany, to explore establishing a travel corridor.
Leung stressed that any reopening of borders and shortening of quarantine periods must be backed by science.
The arrival of cooler year-end weather could make a fourth wave of Covid-19 infections different from the earlier rounds. Experts said winter allowed viruses to survive longer and spread faster between people.
Dr Joseph Tsang Kay-yan, co-chairman of the Hong Kong Medical Association’s advisory committee on communicable diseases, said the weather could result in sick people having more nose and throat secretions, and Covid-19 could spread as they cough and sneeze.
He said even though having both the flu and Covid-19 might not increase the transmissibility of the coronavirus, a patient might get a more severe condition affecting multiple organs such as the heart, lungs and brain.
The population has very low herd immunity even though we have had about 5,000 cases
Professor Yuen Kwok-yung
Leung said a flu jab was therefore all the more necessary this year, and called for mass vaccinations to cover about 60 per cent of the population, up from about 10 to 20 per cent each year.
Vaccination could also help doctors diagnose Covid-19 infections faster and relieve bed shortages at public hospitals, Leung said.
There were 182 intensive care admissions and 113 deaths during Hong Kong’s most recent flu season from December last year to January this year.
While some have expressed worries that the coronavirus might mutate into a more virulent strain in winter, Dr Gilman Siu Kit-hang, an associate professor in Polytechnic University’s department of health technology and informatics, believes Covid-19 gene mutations have stabilised, with a major strain dominating across the world since March.
He said the next major event likely to trigger a significant mutation of the virus would probably be the arrival of Covid-19 vaccines, which would force the virus to adapt and change.
Siu also said the Covid-19 pathogen was unlikely to develop into a stronger strain by swapping genetic material with the seasonal flu bug in a process called recombination, as coronaviruses usually only did that with each other.
“But even if a reshuffling occurs, it may come out weaker than before, like how the Sars virus became less transmissible after recombining with another coronavirus,” he said, referring to the severe acute respiratory syndrome outbreak of 2003.
Professor Yuen Kwok-yung, a HKU infectious disease expert, was concerned that social-distancing measures were being eased at a time when there was a general fatigue among the public, who had been living with the curbs for most of this year.
Hong Kong was also not yet anywhere near achieving herd immunity, when a large enough number of people – about 60 per cent of the population – become immune to Covid-19, making it less likely to spread.
“The population has very low herd immunity even though we have had about 5,000 cases,” Yuen said.
More from South China Morning Post:
- Coronavirus: Hong Kong’s fourth wave ‘could be the worst yet’ as city aims for enough Covid-19 vaccine shots to cover double city’s population
- Hong Kong confirms five new Covid-19 cases; health officials ask police to help track down bar patrons as fears emerge of new cluster
This article Coronavirus: when will Hong Kong’s fourth wave of Covid-19 hit? Very soon, experts warn first appeared on South China Morning Post