The Chinese special administrative region of Hong Kong, along with mainland China, has among the most stringent Covid-19 restrictions in the world, which includes required hotel quarantine for all arrivals. While a devastating fifth wave of infections has subsided, social-distancing measures have been eased, and vaccination rates have climbed, case numbers have been rising, raising questions among the public and outsiders wishing to travel to city about the outlook for Hong Kong as it continues to wrestle with the pandemic. Drs Ivan Hung Fan-ngai, David Christopher Lung, Siddharth Sridhar and Yuen Kwok-yung of The University of Hong Kong assess the situation and, in anticipation of a sixth wave, offer recommendations for Hong Kong to move towards hybrid immunity and return to normalcy.
Measures such as extensive testing buy time for vaccination, allowing Hong Kong to push ahead along the endemic route and, eventually, open to the rest of the world (Credit: Lewis Tse / Shutterstock.com)
As Covid-19 cases climb in Hong Kong, the new administration of the Chinese special administrative region (SAR) has quickly signaled its determination to control the spread of the infection. The public has welcomed the government’s focus on improving people’s access to mainland China while also opening up Hong Kong to the world. But the devil is in the details. As we wait for the government to unveil proposed initiatives, it would be helpful to review the lessons learned from the past three years of fighting the pandemic, our ups and downs, trials and tribulations.
Governments around the world have to devise their epidemiological control measures based on science as well as other considerations. But decision making needs to start with the basics of scientific findings and informed extrapolations. Hong Kong is blessed with a robust research community on infectious diseases, whose members include practicing doctors. Our researchers are also rooted in scholarship on fighting diseases – the plague more than a century ago (1894) and, more recently, the H5N1 avian flu (1997), the severe acute respiratory syndrome known as SARS (2003), the H1N1 swine flu (2009), and the H7N9 avian flu (2013). With Covid-19, Hong Kong researchers have been making significant breakthroughs, thanks no less to their close collaboration with the local public hospital system, as well as counterparts in mainland China and around the world.
Hong Kong had a major outbreak of the Omicron BA.2 variant of Covid-19 at the beginning of this year. Four million to five million people are estimated to have been infected. (A University of Hong Kong data model predicted that the peak of the coronavirus’s fifth wave would be reached in early March, with a tenfold drop in infections a month later, as did indeed happen.) After a rapid drop in the number of cases in April, daily numbers have been increasing slowly, rising to and plateauing at around 3,000 recorded infections a day in the first half of July, which coincided with a significant drop in neutralizing antibodies.
But as Hong Kong people now understand through personal experience or daily media reports, case numbers alone should not be a cause for alarm. On the contrary, several indicators show that Hong Kong’s Covid situation is in fact moving to endemicity. First, Omicron has evolved to become much more flu-like in terms of morbidity and mortality. High infection rates in conjunction with rising vaccination rates ensure that there is a high level of hybrid immunity (i.e., acquired from both prior infection and vaccination) in the community. Vaccines should soon be approved for those aged from six months to three years, which would open the way to reaching an even higher level of immunization.
Second, we now have highly effective oral antiviral treatments readily available for treatment of early Covid infections to prevent progression to severe disease. While the number of hospitalizations has doubled since the beginning of June from 500 to 1,000 cases, we still have very few severe cases or deaths, which are mainly related to unvaccinated or incompletely vaccinated individuals, with the majority being elderly with chronic illnesses.
Finally, Omicron-matched boosters are expected to be available at the end of this year. This would be important for individuals at risk of severe Covid. We even have a second-generation Omicron-matched vaccine under clinical trials right here in Hong Kong. These trials are progressing well and the vaccine should be available for use towards the end of this year.
Existing vaccines retain excellent effectiveness against severe forms of Omicron. Studies have shown that three doses of the two vaccines in Hong Kong, the BioNTech mRNA vaccine and the inactivated Sinovac vaccine, are highly effective in protecting against severe illness and death from Omicron.
It is heartening that vaccination rates have been rising since the onset of the fifth wave in late December 2021. We now have close to 93 percent of the population vaccinated with their first dose and 90 percent with a second dose. We still have a lot to do to increase the percentage of people who have received a third dose, which is around 66 percent. We will need to work hard to push that higher over the next two months, particularly among the elderly.
There is considerable media attention on newer Omicron subvariants such as BA.4, BA.5 and BA2.75. Although these variants appear to have an advantage over other Omicron subtypes in terms of transmissibility and/or immune evasion, there is currently no evidence that they are causing more severe disease compared to previous variants. Indeed, prior Covid vaccination and infection strongly protects against a severe form of Omicron, irrespective of variant. Looking at the experience of other places around the world that have had sequential BA.1 > BA.2 > BA.2.12.1, BA.2.75, BA.4/5 waves, it is unlikely that Hong Kong will experience a repeat of the very severe fifth wave, which paralyzed our healthcare services, leading to 9,000 deaths. This is so long as we do not see another immune-evasive variant which also has high intrinsic virulence, or a virulent antigenically drifted influenza virus. Even in the event of a surge in intensive care unit (ICU) occupancy, the measures used for previous winter flu surges are adequate as long as sufficient stockpiles of test and antivirals are ready.
Covid-19 is here to stay
SARS-coronavirus-2 will never disappear off the face of the earth. It will continue to infect humans similar to the four other human coronaviruses (OC43, 229E, NL63 and HKU1). But Its clinical and epidemiological impact will decrease with time when the anti-severe-disease hybrid immunity (mucosal + T cell) in our global population, including Hong Kong and China, is solidly established after repeated rounds of vaccination (neutralizing antibody + T cell) and natural infection (mucosal + neutralizing antibody + T cell). Covid-19 is different from a serious flu, but the reality is that it is becoming endemic almost everywhere in the world.
All of the coronaviruses tend to infect the upper respiratory tract and often cause asymptomatic or mildly symptomatic infection in healthy individuals who have been previously infected or fully vaccinated. The mortality of SARS-CoV-2 is now only between 0.1 percent to 0.2 percent for the fully vaccinated. But mortality among the elderly and chronically ill who require hospitalization can go up to 9.1 percent and even to 25 percent for non-Covid-19 coronaviruses with no antiviral treatment. The rate is expected to be lower for SARS-CoV-2 patients who need hospitalization and have antiviral treatment.
Thus, the most reasonable course of action is to achieve hybrid immunity as soon as possible so that life can go back to normal. Measures such as extensive testing of incoming travelers, high-risk people and symptomatic patients; contact tracing; case isolation; contact quarantine; and social distancing only buy time for vaccination, which allows us to push ahead along the endemic route, paving the way for opening Hong Kong to the rest of the world.
To achieve the most protective hybrid immunity before winter so as to avoid another catastrophic collapse of our healthcare system, we should continue to relax gradually our social-distancing measures so that the background immunity of our population against severe Covid is constantly boosted by natural infection with Omicron sub-variants including BA.2, BA.2.12.1, BA.2.75 or BA.4/5, while we await an Omicron-specific booster.
We need to protect the unvaccinated population during the period of relaxation over the summer to boost our hybrid immunity. Unvaccinated high-risk individuals should always wear better respiratory protection such N95 facemasks or their equivalent when going out and should not attend mask-off activities. All family members with unvaccinated individuals should do daily rapid antigen tests (RATs) so that reverse isolation or early antiviral treatment of the exposed high-risk unvaccinated individual can be instituted rapidly.
What should be the focus or priority of our anti-epidemic measures now before full relaxation in Hong Kong? Note that Singapore has vaccination rates – one dose (93 percent), two doses (92 percent) and three doses (78 percent) – which are better than Hong Kong’s. So, taking from the Lion City’s experience, our priority should be the enforcement of vaccine passes especially at markets and supermarkets so that the elderly in the community outside residential homes will get vaccinated.
What would we anticipate when all social-distancing measures are relaxed and incoming travelers are simply home-quarantined? From Singapore’s experience, we would expect the daily number of cases to fluctuate between 3,000 and 21,000 (adjusted to the population of Hong Kong, which is seven million people). The number of hospitalizations requiring oxygen supplementation at the peak would be about 100. Deaths would mainly relate to incomplete vaccination and a very severe underlying disease. It is always better to step down social distancing and border control during the summer when environmental survival and airborne transmission of the virus is lower, as would be inflammatory damage from infection.
Vaccination, vaccination and vaccination
The key focus is to maintain the population’s immunity against severe diseases by vaccination boosting and by a low level of natural infection (less than 17,000 cases a day is the threshold in Singapore with continued testing and numbers reporting). Simply put: Everyone should get vaccinated, especially the very young, the elderly and the chronically ill. Vaccine-pass use should be maintained until another winter has passed.
Pharmaceutical interventions by antivirals should replace non-pharmaceutical interventions such as social distancing, except that universal masking in indoor settings should always be maintained to reduce the dose of virus exposure. The stockpile of molnupiravir and paxlovid should be deployed efficiently in government outpatient clinics, private clinics, hospitals and elderly homes during the inevitable sixth wave to reduce the burden on public hospitals. For individuals with mild infection, care should be decentralized to the community and elderly care homes as much as possible.
As a large proportion of children across all age groups in Hong Kong were also exposed to Covid-19 during the fifth wave, we expect that this baseline immunity would offer strong protection from severe Covid disease outcomes, thereby driving rates of severe disease in this population to levels comparable to winter flu seasons in the past. We also hope that the Comirnaty (BioNTech Pfizer) vaccine will be approved for the six months-to-4 years age bracket soon, which will give parents an additional line of defense against severe Covid.
We have been testing Omicron-matched vaccines, including both the Sinopharm and Sinovac-CoronaVac versions, at the clinical trial center at The University of Hong Kong. We aim to complete our study in two months and have some results to share by the end of October. We hope to use this vaccine or the BioNTech mRNA vaccine so that the people in Hong Kong will be able to choose between new Omicron mRNA and inactivated vaccines, which should be able to boost our immunity against the Omicron variant better than the first generation did.
Questions going forward
Our border policy should prioritize opening with the rest of the world as the mainland continues its zero covid-19 policy. We should gradually shorten the quarantine period to home quarantine with a RT-PCR test at arrival, the first three days and the tenth day and daily self-administered RATs. The home and hotel quarantine could eventually be replaced by daily RT-PCR testing with a bracelet tracker for seven days and another test on the tenth day. Inbound travelers would be forbidden by the modified government’s LeaveHomeSafe vaccine pass app from visiting restaurants and pubs for the first seven days. Cross infections do occur in quarantine hotels since they are not hospital isolation rooms.
Imported cases from travelers does not make a difference to the local epidemic situation. As all returning travelers are required to be fully vaccinated, they would not place undue burden on our hospital system even if they have Covid.
Antigen and/or RT-PCR testing should be deployed in clinically/epidemiologically sensitive settings such as dedicated border facilities, hospitals, clinics and elderly homes. The public should be encouraged to self-administer an RAT whenever they suspect they may have Covid-19. Higher risk individuals can procure antivirals from designated clinics and private-sector outlets and can self-isolate at home.
The use of restriction testing declarations (RTD), or the issuance of compulsory testing notices, is expensive, disruptive and wasteful. They should now be abandoned because we DO want a low level of virus circulation to boost our airway mucosal immunity.
Existing influenza surveillance mechanisms can be easily modified for Covid-19 in schools, childcare facilities and kindergartens. The daily Covid antigen testing for schools should be cancelled. Parents should know the risks if they do not vaccinate their children for Covid or flu. People will make decisions after weighing the amount of risk they would like to take.
RT-PCR testing for known variants is generally sufficient. Genome sequencing should be limited to infected incoming travelers, outbreaks or academic settings to detect for emerging variants or subvariants.
Contact tracing should be limited to epidemiologically sensitive settings such as inpatient facilities, kindergartens, playgroups and elderly homes. The purpose of outbreak investigation is to prescribe antivirals quickly to newly diagnosed cases with risk factors. Contact tracing in restaurants and bars are just ways to maintain training of the contact tracing team, keep up public vigilance, and identify premises with poor ventilation.
Hospital isolation should only apply to epidemiologically sensitive settings or for new variants when their epidemiological or clinical significance are still uncertain. Patients who acquire Covid-19 in the community should be encouraged to self-isolate at home. Isolation in community isolation facilities should be offered to cases who have close contacts who are at-risk for severe Covid and those living in cramped conditions. The same principle should apply to quarantine. We should not have different rules for different variants. The variants BA 2.12.1, BA.2.75, BA.4, and BA.5 may cause more cases but their impact on the healthcare system is going to be much milder than during the fifth wave. As noted earlier, we should stop hotel quarantine for incoming travelers soon.
We have to admit that the social distancing measures that we have adopted in the first two years of the pandemic were not as effective during the fifth wave. These social distancing measures (except universal masking unless exercising outdoors) are therefore no longer necessary unless there are sharp increases in the number of hospitalizations, ICU admissions or deaths, irrespective of variants or viruses. We should gradually relax all these measures, following the example of Singapore.
We should refocus our vaccination and booster campaigns on the elderly and those with chronic medical conditions. The use of the vaccine pass should only be relaxed after the coming sixth wave. By then, close to 100 percent of the population will be either infected, fully vaccinated ,or both.
When new variants come in from other places, if most of the population is either infected or vaccinated or both, these new strains are unlikely to have an impact. Even an antigenically distinct variant such as Omicron did not change the hospitalization rates in South Africa, India and Europe. Case counts will continue to fluctuate, but the situation will be manageable. We should not go back to imposing a 14/21-day quarantine. A growing number of positive tests should not a cause for concern. Increasing hospitalizations, ICU admissions and deaths will occur in the beginning of the sixth wave but will be far lower than fifth-wave levels.
New variants with varying degree of immune escape will continue to emerge but the disease should be mild as the full vaccination rate would hopefully be over 95 percent and hybrid immunity over 70 percent. By that time, large-scale RT-PCR testing for case finding and surveillance should be abandoned, reserving it only for guiding clinical management. Testing would only be indicated in symptomatic individuals who have risk factors for severe disease or require hospitalization so that antiviral treatment can be administered rapidly. Accommodating infected cases in wards by cohort would be sufficient, and infection control requirements should be relaxed further as the vaccination rates would be high enough and the population would have a sufficient level of hybrid immunity. This will help free up hospital bed space and allow staff in public hospitals to clear the long queue of patients that built up as a result of the suspension of non-urgent services in the past three years.
Contact tracing should be limited to cases infected by new variants with uncertain behavior. Even now, we should let healthcare workers with a history of contact and who test negative to be on duty to avoid the vicious cycle of decreasing hospital manpower amid rising cases in the community. There should be yearly vaccine boosting against the latest variant for the elderly and chronically ill, on top of the administration of the seasonal flu vaccine.
Then, life should almost be back to normal.
Further reading (editor’s selections):
Chan, Yuen-ying. (March 24, 2022) “China’s Omicron Conundrum: Stress Test for the Zero-Covid Strategy”, AsiaGlobal Online, Asia Global Institute, The University of Hong Kong.
Lung, David Christopher; Sridhar, Siddharth; and Yuen, Kwok-yung. (March 17, 2022) “Riding Out Hong Kong’s Omicron Storm: The Consequences of Inaction”, AsiaGlobal Online, Asia Global Institute, The University of Hong Kong.
Yuen, Kwok-yung; Lung, David Christopher; and Hung, Ivan Fan-ngai. (January 6, 2022) “The Road to Reopening Hong Kong”, AsiaGlobal Online, Asia Global Institute, The University of Hong Kong.
Ivan Hung Fan-ngai
The University of Hong Kong
David Christopher Lung
The University of Hong Kong
The University of Hong Kong
The University of Hong Kong