The benefit of isolating discharged COVID-19 patients is doubtful, said Siddharth Sridhar, clinical assistant professor in microbiology at HKU,  who cited research data from mainland China to support his observation.

Sridar also warned the public that under current government policy, being diagnosed with COVID-19 in Hong Kong now comes with a very very long confinement period.

“Please get vaccinated to protect yourself from COVID-19. Vaccinated people are less likely to catch Delta variant COVID-19 than unvaccinated individuals,” said Sridhar.

Sridhar made the call in the following analysis on his Facebook page posted on 30th October 2021.

Last week, Hong Kong announced new discharge criteria for patients with COVID-19, bringing it in line with the policy of mainland China. One part of the criteria is that patients who test negative for SARS-CoV-2 by consecutive RT-PCR tests will still require 14 days of isolation at the Hong Kong Infection Control Centre (HKICC). This means that anyone diagnosed with COVID-19 in Hong Kong will now have to spend a minimum of 24 days in the hospital and isolation facilities. In reality, hospitalization is likely to be even longer than this for many patients.

The 14-day post-discharge isolation requirement has been a longstanding mainland infection control policy for COVID-19. Early on in the pandemic, Chinese doctors and epidemiologists observed that a proportion of recovered COVID-19 patients became ‘re-positive’ i.e. their RT-PCR tests became positive once again shortly (within 4 weeks) after discharge despite consecutive negative tests at discharge. This phenomenon is quite common and occurred in 10 – 20% of all COVID-19 cases. Several reasons are postulated for this, some of which are:

1) False-negative RT-PCR tests before discharge

2) False-positive RT-PCR tests after discharge

3) Residual non-infectious viral nucleic acids in the upper airway

4) Recrudescence of the infection despite initial recovery

5) Reinfection within short time of recovery

Reasons 4 & 5 above are big concerns because that would mean seemingly recovered patients shed virus and potentially infect others. This led to a fear that these ‘re-positives’ were potentially infectious. Therefore, a system of post-discharge isolation was created in the mainland to detect re-positive patients and subject them to longer medical observation.

Chinese scientists have continued to conduct extensive research into this. So, what are their latest conclusions on the golden question: ‘Are re-positive cases infectious?’

I include some high-quality studies on this topic in the table below. In general, the findings are as follows:

1) ‘Re-positive’ patients generally show improving symptoms and imaging findings;

2) Such patients also have robust antibody responses similar to non-re-positive patients, which indicates that reinfection in such a short time frame is an unlikely cause for them turning re-positive;

3) Their viral loads are low, much lower than the original admission. Studies (Yang C et al, Lu J et al in table below) that attempted next generation sequencing tend to only find genome fragments rather than whole genomes, which would indicate non-infectious viral nucleic acid rather than complete viral particles;

4) Studies that attempted cell culture fail to recover any infectious virus from re-positive patient samples;

5) Most importantly, epidemiological studies (Yang C et al and Chen SL et al in table below) failed to find any onward transmission from re-positive patients to close contacts.

I quote the following conclusions verbatim from some of the studies:

1) “Recurrent positive patients pose a low transmission risk, a relatively relaxed management of recovered COVID-19 patients is recommended.” Yang C et al, Emerg Microbes Infect, study by Shenzhen CDC

2) “Re-positive SARS-CoV-2 cases do not appear to be caused by active reinfection and were identified in ~14% of discharged cases. A robust NAb response and potential virus genome degradation were detected in almost all re-positive cases, suggesting a substantially lower transmission risk, especially through respiratory routes.” Lu J et al, EBioMedicine, study by Guangdong CDC

3) “The viral load in re-positive cases was very low; patients were not infectious and the risk of human-to-human transmission was extremely low.” Liang L et al, IJID, study by Guangdong CDC

4) “Our data suggest that the short-term recurrence of positive SARS-CoV-2 RNA in discharged patients is not a relapse of COVID-19, and the risk of onward transmission is very low.” Chen SL et al, OFID, study from universities in Guangdong

5) “This retrospective study in Wuhan analyzed the basic characteristics of recovered COVID-19 patients with re-positive PCR test and found that these cases may not be infectious.” Wu X et al, BMC Medicine, study from Wuhan CDC & others

Note that the above applies to immunocompetent patients. Some immunocompromised are known to harbor potentially infectious COVID-19 for long periods of time (although they would not be expected to test negative and then re-positive).

Furthermore, there is no 100% certainty in science and short-term re-infection is theoretically possible although extremely uncommon (Abu-Raddad LJ et al, Clin Infect Dis). One case report from Portugal claims that a re-positive healthcare worker infected others (Correia AM et al, IJID) although there are uncertainties in the interpretation of the study. But, on the whole, these large studies published from China strongly indicate that the vast majority of re-positive patients are not infectious.

Therefore, the benefit of post-discharge isolation of COVID-19 patients to public safety is doubtful. This policy is also difficult to sustain when Hong Kong faces an inevitable future wave of COVID-19. Unlike the mainland, we do not have unlimited land and manpower resources for quarantine facilities when there is a large local outbreak (and such resources are probably better prioritized elsewhere anyway).

In any case, please note that being diagnosed with COVID-19 in Hong Kong now comes with a very very long confinement period. Please get vaccinated to protect yourself from COVID-19. Vaccinated people are less likely to catch Delta variant COVID-19 than unvaccinated individuals.

HKU’s medical faculty will administer free vaccinations for the public starting from 16 March, Tuesday, as part of the government’s community wide vaccination programme. The faculty has also launched six research projects on various aspects of the vaccines, and is recruiting volunteers the pioneering studies.

HKUMed is responsible for the Community Vaccination Centre at Ap Lei Chau Sports Centre which will offer the COVID-19 mRNA Vaccine: Comirnaty (BNT 162b2) from Fosun Pharma/BioNTech.

For details of the APL vaccination centre, see  https://www.med.hku.hk/en/covid-19/vaccine To sign up for taking the jab at the ALC center, go to the HK government booking page. Pick Southern District, and  Ap Lei Chau for venue.

For directions to the ALC centre, see https://www.youtube.com/watch?v=Zt_Fllhl4wg

Volunteers are needed for a vaccine allergy tracking study, and a study on the effect of combining two kinds of vaccines.  See here for details of the research projects and ways to sign up for the research.

News report in Chinese media  HK01

Chinese version of this article was published in Ming Pao on 25th December 2020

Written by David Lung, Honorary Assistant Professor; Kelvin Chiu, Honorary Assistant Professor; Siddharth Sridhar, Assistant Clinical Professor; and Yuen Kwok-Yung, Chair Professor,  of the Department of Microbiology, Li Ka-shing Faculty of Medicine, HKU. 

The article is published under Creative Commons license CC BY-ND 4.0 . Click on link for share conditions.

The objectives of this COVID-19 vaccination program

A high uptake of effective SARS-CoV-2 vaccines is likely to significantly control  the COVID-19 epidemic in Hong Kong by accelerating herd immunity against the virus (Ref 1). This will minimize the morbidity, mortality, burden on healthcare and quarantine facilities, and the financial burden on the government. Moreover, normal socioeconomic activities and overseas connections can be restored.  Hong Kong should aim to vaccinate the entire population within the shortest possible time frame. As clearly seen in various regions around the world, achieving and sustaining zero COVID-19 cases is very challenging.  Border control is not leak-proof because 2.5 to 5% of imported cases have an incubation period of less than 14 days. Many COVID-19 patients may not have symptoms, thereby spreading the virus to those around them unknowingly. Even for those who seek testing, there is a small possibility of COVID-19 patients having false negative test results due to suboptimal sample collection. Compliance to specific counter-measures at critical control points by businesses and the public cannot be fully enforced. Therefore, the SARS-CoV-2 vaccines provide an additional critical layer of protection to sustainably suppress COVID-19 in Hong Kong.

This urgently needed vaccination program cannot be successful without complete transparency to win the support from the general public. The choice of each individual on both the timing and type of vaccines to be administered must be respected.

Acknowledging the unknowns and limitations of the three vaccines

It must be acknowledged that coronavirus vaccines have never before been administered to humans outside study settings. Furthermore, two of the three vaccines bought by Hong Kong are based on new technologies which have never been used in our routine immunization program. Their emergency use must be authorized and carried out according to the best international practice with continuous monitoring of their safety, quality and efficacy after launching of this program.

We know from animal studies that all three vaccines induce sufficient serum neutralizing antibodies which largely protect recipients from symptomatic COVID-19 and complications, but may not necessarily stop asymptomatic virus infection, shedding and transmission in the upper airway. Moreover, we do not know the duration of protection after vaccination and if there will be a booster vaccination is needed months or years after the second dose.

Allergic reactions to residual or stabilizing chemicals inside the vaccines are inevitable. Thus the checking of the history of allergy is mandatory for every consenting recipient.

Furthermore, some rare and serious side effects may not be detected with 10,000 vaccinees in study settings, but may be detected when vaccination is carried out on a large scale involving millions of people. These rare autoreactive inflammatory complications such as transverse myelitis, Guillain barre syndrome, and others usually present within 6 weeks after vaccination. It must be emphasized that these serious side effects are extremely uncommon after usually-administered vaccines.

The vaccines to be available in HKSAR (See table 1)

Table 1: Available COVID19 vaccines in Hong Kong SAR

About 18 COVID-19 vaccines have reached phase 3 clinical trials. Many of these candidates have published promising data showing that they are immunogenic in animals & in phase 1/2 human clinical trials. These data have been scrutinized by experts at scientific committees of the HK government’s Centre for Health Protection. The government has taken reference from experts and decided to make a number of advanced purchase agreements to get twice the number of vaccines for our 7.5 million population. These vaccines include the CoronaVac (inactivated whole SARS-CoV-2  virion vaccine of Sinovac), the AZD1222 (Oxford-AstraZeneca modified chimpanzee adenovirus vector 1 with spike of SARS-CoV-2), and the Tozinameran BNT162b2 (mRNA vaccine encoding spike of  SARS-CoV-2 from BioNTech/ Pfizer).

Constituents of the vaccines and their mechanism of action (see table 2) (ref. 2,3,4,5)

Table 2: Ingredients and Track Record of different vaccines

The coronaVac contains all the full antigens of the full virion particle including the surface spike, membrane, envelope, abundant nucleocapsid proteins, RNA genome and aluminium hydroxide adjuvant (Ref 2). The exact list of excipients in the vaccine is yet to be announced, but like all inactivated virus vaccines, the vaccine is likely to contain minute quantities of residual proteins from cell culture ingredients (eg. cell debris), chemicals for inactivation (eg. beta-propiolactone) and stabilization.  The injected vaccine proteins are taken up by host dendritic cells and macrophages which present the antigens to the lymphocytes. It is likely that vaccination will stimulate mainly a T helper 2 response with a good neutralizing antibody titre directed towards the Spike protein. There would also be non-neutralizing antibodies generated against other internal viral proteins of SARS-CoV-2.

The AZD1222 contains a non-replicating chimpanzee adenovirus encoding the SARS-CoV-2 spike protein. Despite the purification process, minute quantities of residual cell culture ingredients (cell debris) and chemicals for lysis (such as triton 100, likely remain in the vaccine.  AZD1222 cause non replicating infection of host cells by the chimpanzee adenovirus which also express SARS-CoV-2 spike. Both adenovirus proteins and SARS-CoV-2 Spike are then recognized by dendritic cells to trigger a Th1 immune response with neutralizing antibody, cell mediated CD4, and cytotoxic CD8 lymphocyte responses against the adenovirus proteins and the SARS-CoV-2 spike protein. Note that there would be neutralizing and non-neutralizing antibodies produced against the Spike and other adenoviral proteins.

Tozinameran BNT162b2 contains the modified RNA of SARS-CoV-2 spike encapsulated in pegylated lipid nanoparticles (0.1 micron diameter) which facilitate RNA entry into host cells. The spike protein is expressed and presented to host immune cells leading to Th1 immune response with neutralizing antibody, cell mediated CD4 and cytotoxic CD8 lymphocyte response against the SARS-CoV-2 spike protein. The vaccine will contain a minute amount of residual enzyme proteins, double stranded RNA and unused nucleoside triphosphates despite purification but will be free of animal components. Note that the polyethylene glycol polymer for encapsidating the RNA can be a source of allergy in humans.

The immunogenicity of the vaccines in phase 1 or 2 clinical trials (table 3) (Ref. 6,7)

Table 3: Comparison of clinical efficacy of vaccines based on phase III clinical trial data

Direct comparison of the immunogenicity of these three vaccines is difficult as there has never been a head-to-head comparison, but it is obvious that Tozinameran BNT162b2  induced higher neutralizing antibody titre than that of the convalescent asymptomatic patients, As for the induction of cell mediated immunity, the Interferon gamma ELIspot test for specific lymphocyte response suggested that Tozinameran BNT162b2  and AZD1222 are better than CoronaVac.

The clinical efficacy of these vaccines in phase 3 clinical trials

Even though the clinical efficacy of CoronaVac is not yet available in the public domain, it is highly likely that this should be much higher than the WHO requirement of over 50%. As for AZD1222, there is uncertainty about the optimal dosing regimen due to the unintended use of a lower dose in a proportion of the vaccine recipients, which requires further confirmation by further clinical trials. But the preliminary estimated clinical efficacy is 90% for those with a low dose priming and full dose boosting, whereas a full dose of priming followed by a full dose boosting has a lower clinical efficacy of 70.4%. As for Tozinameran BNT162b2, its overall clinical efficacy is 95% with over 90% protection across all age groups from 16 to over 75.

The track record of the technology platforms used by of these vaccines

With regards to the vaccine platform, inactivated whole virion vaccines such as CoronaVac has the best historical track record in terms of clinical efficacy, experience and safety. In fact, our presently used polio, rabies and hepatitis A vaccines are all manufactured by this technology.  There are theoretical concerns that this approach may be associated with more of a Th2 immune response after encountering the wild type virus which may lead to lung immunopathology with eosinophilic response although this did not occur in monkey models where the vaccine was highly effective in preventing severe COVID-19. Another theoretical concern is antibody dependent enhancement of infection, which happens especially when the neutralizing antibody titre decreases over time, although this theoretically applies to any vaccine platform.

The adenoviral vector technology (AZD1222) has been used in tackling the Ebola outbreaks in Africa but this has never been used widely in routine immunization program.

The mRNA technology (Tozinameran BNT162b2) has no post-marketing track record both in terms of clinical efficacy and safety.

The safety of these vaccines in phase 3 clinical trials (table 4)

Table 4: Comparison of safety profile of vaccines

The side effects profiles of all 3 vaccines are mild and acceptable. Besides the rate of fever is lowest for coronaVac (3.3%), AZD1222 (18%), and Tozinameran BNT162b2 (14.2%), coronaVac also has the lowest rate of other symptoms amongst these 3 vaccines.

Two cases of transverse myelitis were reported amongst 7174 AZD1222 vaccine recipients although one was attributed to undiagnosed multiple sclerosis. At this stage, the AZD1222 has not yet been approved widely.

A few cases of type 1 immediate hypersensitivity with skin rash and wheezing was reported in Tozinameran BNT162b2 vaccines during recent vaccination campaigns in UK and US. These were attributed to inevitable exposure to the polyethylene glycol (PEG) in our daily food, drug and topical cosmetics which leads to formation of anti-PEG antibodies.

Quality concerns

To ensure the quality of these vaccines, random sampling of each batch should be rapidly performed to exclude contamination of coronaVac and AZD 1222 from adventitious viruses, replication competent adenovirus, and mycoplasma by next generation sequencing.  Electron microscopy can be performed to check the number of spikes, integrity of the inactivated whole virions or the morphology of adenoviral vector vaccine. High performance chromatography and mass spectrometry, protein gel electrophoresis and quantitative PCR with or without reverse transcription should be performed to ensure there is no excess unwanted chemicals or degradation of the viral RNA or target virus proteins.  Endotoxin assay and culture test for sterility should also be performed.

How should we launch this vaccination campaign?

The Department of Health has all the regulatory power to authorize the emergency use of these 3 vaccines after going through due committees and legislative procedures. Vaccination centers, hospitals and clinics with the necessary cold chain and storage, resuscitation facilities, and medical personnel should be the sites where these vaccines should be administered.

Information technology system should be in place to monitor for safety, efficacy and quality of these vaccines, and the health status of the vaccinees identified by their ID card number during and after the vaccination campaign. Regular batch to batch monitoring of the chemical and microbiological constituents of these vaccines is important to give confidence the public. Any incidents must be immediately conveyed to the general public.

Public education campaign should be launched with all the information available to ensure 100% transparency, and that the vaccination is completely voluntary and free of charge. The public must be educated to understand that illness and deaths occur daily with or without vaccination. Illness or deaths soon after vaccination may not have any causative relationship. There are 15 to 20 Bell’s palsy per 100,000 population per year compared with the extrapolated 11 cases per 100,000 vaccinees (4 out of 38,000 vaccinees in the trial).

CoronaVac appears to be the safest vaccine with minimal side effects and should be well tolerated by elderlies and those with comorbidities. However, due to the relatively lower neutralizing antibody titre and cell mediated immune response, the duration of protection of coronaVac could be shorter. But this could be compensated by future booster vaccination if the serum antibody levels wane with time.

At this stage in time, the available phase 2 and 3 clinical trial data showed that Tozinameran BNT162b2 appears to have proven clinical efficacy and reasonable safety. The content in this vaccine is relatively simple and chemically homogeneous which can be checked easily by laboratory assays.

Thus, Tozinameran BNT162b2 and coronaVac should be lined up as the first-choice vaccines used in HKSAR. Healthcare workers, elderlies, patients with chronic underlying disease, and those at border control and high risk occupation should come first to receive Tozinameran BNT162b2 or coronaVac. They should be given the choice to choose the type of vaccine.

Though the two cases of transverse myelitis could be just bad luck, it is prudent to wait for a longer time till a more proper phase 3 clinical trial of AZD1222 is performed as there is still confusion over the optimal dosing regimen.

We do not have the scientific data on the effect of using 2 different types of SARS-CoV-2 vaccines in one individual. In order not to confuse the effects of different vaccines, it is prudent that no recipient should receive any other vaccines within 6 weeks before and after receiving SARS-CoV-2 vaccination.

The history of allergy should always be checked to ensure that those with allergy to residual chemicals in coronaVac and AZD1222 (such as penicillin, streptomycin, bovine serum albumin) should not be given these vaccines and be considered for Tozinameran BNT162b2. Note that the incidence of type 1 hypersensitivity to penicillin is 0.02% to 0.04%. Those with history of allergy to PEG should be given coronaVac or AZD1222. Clinical immunologists with experience in doing skin test should help those with uncertain history of allergy before deciding on the type of vaccine used (see skin test photos, Ref. 8).

Reference list

1. Fontanet, A., & Cauchemez, S. (2020). COVID-19 herd immunity: where are we?. Nature reviews. Immunology, 20(10), 583–584. https://doi.org/10.1038/s41577-020-00451-5
2. Gao Q, Bao L, Mao H, et al. Development of an inactivated vaccine candidate for SARS-CoV-2. Science. 2020;369(6499):77-81. doi:10.1126/science.abc1932
3. Vaccines and Related Biological Products Advisory Committee Meeting. December 10, 2020. FDA Briefing Document. Pfizer-BioNTech COVID-19 Vaccine. bit.ly/3mN7Lb4 （Accessed on 21 Dec 2020）
4. Polack FP, Thomas SJ, Kitchin N, et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine (published online ahead of print, 2020 Dec 10). N Engl J Med. 2020; 10.1056/NEJMoa2034577. doi:10.1056/NEJMoa2034577
5. van Doremalen N, Lambe T, Spencer A, et al. ChAdOx1 nCoV-19 vaccine prevents SARS-CoV-2 pneumonia in rhesus macaques. Nature. 2020;586(7830):578-582. doi:10.1038/s41586-020-2608-y
6. Mulligan MJ, Lyke KE, Kitchin N, et al. Phase I/II study of COVID-19 RNA vaccine BNT162b1 in adults. Nature. 2020;586(7830):589-593. doi:10.1038/s41586-020-2639-4
7. Voysey M, Clemens SAC, Madhi SA, et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK (published online ahead of print, 2020 Dec 8). Lancet. 2020; S0140-6736(20)32661-1. doi:10.1016/S0140-6736(20)32661-1
8. Folegatti PM, Ewer KJ, Aley PK, et al. Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial [published correction appears in Lancet. 2020 Aug 15;396(10249):466] [published correction appears in Lancet. 2020 Dec 12;396(10266):1884]. Lancet. 2020;396(10249):467-478. doi:10.1016/S0140-6736(20)31604-4
9. Zhang Y, Zeng G, Pan H, et al. Safety, tolerability, and immunogenicity of an inactivated SARS-CoV-2 vaccine in healthy adults aged 18-59 years: a randomised, double-blind, placebo-controlled, phase 1/2 clinical trial [published online ahead of print, 2020 Nov 17]. Lancet Infect Dis. 2020;S1473-3099(20)30843-4. doi:10.1016/S1473-3099(20)30843-4
10. Sellaturay P, Nasser S, Ewan P. Polyethylene Glycol-Induced Systemic Allergic Reactions (Anaphylaxis) [published online ahead of print, 2020 Oct 1]. J Allergy Clin Immunol Pract. 2020;S2213-2198(20)31007-2. doi:10.1016/j.jaip.2020.09.029

Siddharth Sridhar, clinical assistant professor from HKU ’s Department of Microbiology said that the Hong Kong government must take strong and fast action to stop arrivals from the UK or put them under strict supervised quarantine for 21 days.  Sridhar made the call in the following analysis of the latest SARS-CoV-2 variant in the UK published on his Facebook on December 21, 2020.

The new SARS-CoV-2 variant in UK: what do we know so far?

In the last week, we have seen a number of reports on the emergence of a new SARS-CoV-2 ‘mutant’ or variant in the United Kingdom.

RNA viruses such as SARS-CoV-2 mutate continuously. This is perfectly normal and a large number of variants have already been documented since the first emergence of the virus in 2019. The majority of these mutations are ‘neutral’ i.e. they don’t make any significant difference to the transmissibility, infectiousness, and severity of COVID-19. However, once in a while, mutants emerge that really make a difference. A good example is the infamous D614G SARS-CoV-2 variant, which is more transmissible (Hou YJ et al, Science, 2020) and rapidly became the main circulating variant worldwide.

What is VUI 202012/01?

The UK has seen a rapid rise in COVID-19 activity over the last month or so, particularly in South East England. Genetic analysis showed that a new SARS-CoV-2 variant (called VUI 202012/01) emerged around the same time and rapidly took up a large share of circulating variants in the UK. This indicates a possible association between this new variant and increased COVID-19 spread, which is supported by infectious disease modelling analysis. Luckily, there is no evidence so far that VUI 202012/01 causes more severe disease or increased hospitalization. The variant has probably spread widely within the UK and has also been found in Denmark, Netherlands and Australia indicating spread by international travel.

Why are we so worried about VUI 202012/01?

Apart from the tentative association with increased COVID-19 transmission, the variant appears to have mutated more than expected for usually circulating strains. What is particularly worrying is that VUI 202012/01 has accumulated a lot of mutations in its ‘spike’ protein. The spike protein is the part of the virus that is recognised by our immune systems and forms the main target of nearly all approved vaccines to date. The impact of these mutations on the effectiveness of prior immunity or vaccines needs to be rapidly elucidated. Luckily, this is quite easy to do and we should know about the effect of these mutations by the end of January. Until that time, it is crucial to contain VUI 202012/01 and prevent it from gaining a foothold in other countries.

Where does VUI 202012/01 come from?

We don’t know, but given that the number of mutations is more than expected from a normally circulating variant, there are two main possibilities raised by the Europe CDC. The first possibility is prolonged SARS-CoV-2 infection in an immunocompromised person (person with weakened immunity) who then sparked a major outbreak. Such patients have been reported previously and viruses can mutate rapidly in immunocompromised persons (Choi BJ et al, NEJM, 2020). The second possibility is spread from another animal capable of harboring the virus (such as cats or mink). Investigations into this are ongoing. A third possibility that VUI 202012/01 is circulating in humans elsewhere and was imported into the UK is unlikely given the difference between VUI 202012/01 and the thousands of other SARS-CoV-2 sequences in genome databases.

What should we do about VUI 202012/01?

1.HK should act decisively and rapidly to STOP arrivals from the UK until the situation becomes clear. I understand that this is the holiday season and thousands of arrivals are anticipated. However, HK is in a highly precarious situation already with ongoing community transmission and stretched quarantine facilities. We all know that the border control net can never be 100% leak-proof. The introduction of a variant with essentially unknown effects on COVID-19 vaccine efficacy into the city at this juncture would be disastrous. It is a hard decision, but one that must be taken quickly.

2.If arrivals from the UK are not stopped, they must be under strict supervised quarantine for 21 days in government facilities (NOT hotels). Mandatory testing must be done at arrival and at regular intervals during the quarantine.ust be under strict supervised quarantine

We don’t know if VUI 202012/01 is a time bomb. But we must definitely treat it as one.

The towel story:

Infectious disease expert warns of cross-contamination by shared public towels in wet markets

Health tips by HKUMed

As the outbreak begins to subside, it seems that the city may finally relax its stringent preventive measures: public facilities are gradually re-opening, and civil servants are also scheduled to resume regular work arrangements. With this in mind, the School of Public Health at HKU has suggested some health precautions and suggestions for those in the work force, covering potential areas of risks, starting from when you head out to work, to when you return home.

1. Going to work

2. While at work

3. During lunch

4. Getting home

Most importantly, if you are feeling unwell or experiencing any symptoms, avoid going to work and stay home in order to minimise chances of infecting others.

Siddharth Sridhar, clinical assistant professor from HKU ’s Department of Microbiology shared his insights on the risk of Covid-19 re-infection in an article published on his Facebook on 22 August, 2020. Below is the full article.

Can you catch COVID-19 twice?

This question has received a lot of attention. There is fear that immune responses to SARS-CoV-2 infection are weak and temporary, putting millions at risk of re-infection. We have recently heard reports of a young patient in Hong Kong who, on prima facie evidence, appears to have caught COVID-19 twice.

So, what do we know about this? I describe the current evidence on this below. Due to the length of the post (sorry!), references for these points are included in the attached infographic.

1. Most people develop a robust immune response after COVID-19 infection. This response is marked by a surge in antibodies, which then decline to a new baseline as the patient recovers. This response is fairly typical of the body’s response to other viral infections.

2. Some asymptomatic or mildly infected COVID-19 patients have weak antibody responses that decline rapidly, but they still mount a strong ‘T-cell’ response. These T-cells are a critical part of the immune system that we cannot conveniently measure in ordinary labs (unlike antibodies).

3. We know that this immune response persists for at least 3 – 5 months, which is the maximum possible period of observation in studies so far. However, longer-term immunity is entirely possible based on observations in 2003 SARS patients, but will require confirmation from more studies down the road.

4. Does this immune response protect against a second COVID-19 infection? In experimentally infected monkeys and in the Seattle fishing boat study, the answer is YES. Having an immune response against SARS-CoV-2 definitely appears to reduce chances of getting symptomatic re-infection.

5. But what if the virus mutates? Yes, mutations certainly occur, but coronaviruses mutate somewhat less frequently than other RNA viruses. Mutants with complete evasion of host immunity are extremely unusual in the human ‘common cold’ coronaviruses (NL63, 229E, HKU1 and OC43). Most SARS-CoV-2 mutants, including the famous D614G, are not predicted to radically alter the immunogenicity of SARS-CoV-2. Even if they do alter it somewhat, prior exposure is expected to confer some degree of protection.

6. So, the golden question, what is the risk of SARS-CoV-2 re-infection? Based on the above evidence, for most individuals, the first episode of COVID-19 confers a robust immune response, which is likely to be protective against severe symptomatic re-infection, at least in the short term. Genuine re-infection shortly after the first episode is still possible, but is uncommon. The reason why it is still possible is that the human immune response is not ‘all or none’. Instead, it confers a spectrum of protection. In some individuals, such as the elderly, the response tends to be weaker with ‘blind spots’, leading to a chance of re-infection. Such blind spots may be sporadic or due to subtle underlying immune abnormalities.

7. My prediction is that SARS-CoV-2 will permanently circulate in human populations as a new respiratory virus with low death-rate as more and more individuals have some degree of protection (either by natural infection or vaccination). Our amazing immune systems will adapt to this virus and deal with it (hopefully with a bit of help from vaccines).