Clearing the cases to zero, coexistence with virus, two strategies are not contradictory, and all people get vaccinated to end the plague
Since the outbreak of COVID-19 in early 2020, Hong Kong has been fighting the epidemic for about 20 months. Compared with the UK prevalence rate of 9.51% and the mortality rate of 2.03%, the US prevalence rate of 11.23% and the mortality rate of 1.66% (Note 1), the incidence rate in Hong Kong is much lower than that of the UK, the United States and European countries. The prevailing rate in Hong Kong is 0.16%; the mortality rate is about 1.76%.
Local doctors and nurses stay close to their posts. The public medical system can still maintain a high standard of service without paralysis. Patients are also treated in isolation. The success of Hong Kong’s fight against the epidemic is due to the concerted efforts of the local citizens.
In the early stages of the epidemic, surgical masks were widely used, social distancing measures were observed, and border controls were adopted. Subsequently, public hospitals and the private market have greatly improved their detection capabilities in a short period of time, so that people with mild symptoms can be detected early, which will help isolate and track them and prevent the spread of the virus.
The Center for Health Protection has set up a quick contact tracing team and conducted large-scale testing of the entire building where the confirmed case lives or has been visited, so as to isolate all cases and close contacts as soon as possible. Since the emergence of vaccines at the beginning of this year, research reports and experiences of various countries have provided important reference value for Hong Kong's long-term epidemic prevention strategies.
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Containment and clearing is different from extinguishing
In human history, only smallpox was successfully eradicated permanently. Smallpox can be transmitted through the air (basic reproductive number, R0: how many people can be infected by a patient, smallpox R0=5). The skin of the patient has vesicular acne, so it is easy to find and isolate. Eradication of smallpox (eradication) took 184 years from the emergence of an effective vaccine to the complete disappearance of smallpox.
There are many people who are infected with covid without symptoms and can continue to spread covi. Therefore, it is more difficult to fight the disease than smallpox. The goal of containment and clearance is not to eradicate covid but to buy time to vaccinate the entire population.
When foreign countries cannot achieve zero-clearing, it is also difficult for Hong Kong to maintain zero-diagnostics for a long time. In addition, if Hong Kong does not open its borders early and resume economic activities with the mainland and the international community, Hong Kong cannot survive.
The public should seize the space of Hong Kong's current clearance and get vaccinated as soon as possible, so that most people will have a certain degree of immunity and reduce the lethality of the virus.
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Variants destroy herd immunity
Epidemic prevention measures must be adjusted on the spot according to the current epidemic situation. The virus is constantly mutating and epidemic prevention goals must also be changed.
The calculation of herd immunity is based on the basic reproduction rate of the virus, the percentage of the vaccinated population is evenly distributed among all age groups, and the assumption that the vaccine is close to 100% effective (Note 2).
The mathematical calculation of the original Wuhan virus R0=2.5 shows that if a vaccine with an effective rate of about 95% such as Comirnaty is used, only about 70% of the population can be vaccinated to achieve herd immunity. However, the Delta variant (Covi72) that appeared in the middle of 2021 has a significant increase in transmission to R0=7 (Note 3), and the effectiveness of the vaccine has dropped to about 88%.
Calculations show that it takes about 97.4% of the vaccination rate to achieve herd immunity.
The effective rate of Sinovac CoronaVac against Covi72 is about 60%. If the whole population is vaccinated with this vaccine, the threshold for herd immunity is 142.9%. About 40% of Hong Kong's population (those who have been vaccinated) are vaccinated with CoronaVac. Therefore, the required vaccination rate ranges from 97.4% to 142.9% (see the attached figure for the calculation formula).
The vaccination rate of more than 100% may seem counterintuitive at first glance, but this number reflects the continuous evolution of virus strains, increasing transmission efficiency, and reducing the effectiveness of vaccines, greatly increasing the threshold of herd immunity and becoming an unattainable castle in the sky.
In fact, early animal experiments showed that vaccine injection can mainly prevent severe illness (Note 4), but it cannot effectively prevent asymptomatic upper respiratory tract infections.
The protection of the vaccine is in the body. It mainly protects the lungs and fails to reduce the amount of upper respiratory tract virus. Therefore, the infection only decreases but can still continue.
Real-life data of confirmed cases in Hong Kong at the airport and data from other countries show that even those who have completed the vaccination can still be infected, and most people have no symptoms but they can still spread large amounts of live viruses and are infectious (Note 5).
Recent studies published in Singapore and the United States pointed out that people infected with Covi72 after vaccination have the same amount of nasal virus in the early stage as those without vaccination but the virus level declines faster. So the vaccine can shorten the infection period (Note 6). Even if the vaccine fails to effectively reduce the spread of the virus in asymptomatic patients, the two vaccines can still effectively reduce the lethality of Covi72 and prevent severe and death cases after infection.
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Realistic data, learn from experience
Countries with high vaccination rates, such as 60% to nearly 80% of the United States, the United Kingdom and Israel, after relaxing their epidemic prevention measures, the epidemic broke out again. At present, in the UK, the daily number of diagnoses and deaths is approximately 31,000 and 100, respectively; Israel also has approximately 7,400 and 20, respectively, and in the United States there are approximately 146,000 and 960 respectively (Note 1).
Israel is one of the countries with the highest vaccination rate in the world. It has been relaxed since the spring. After the reopening, citizens will travel abroad, but even those who have completed the vaccination can still be infected. In addition, children under the age of 12 have not started vaccination, so after the children return home, the patients can spread the drug at school and cause an outbreak (Note 7).
Using mathematical calculations to estimate the herd immunity threshold and vaccination rate, it is assumed that human-to-human contact occurs randomly, and the vaccinated population is evenly distributed among all age groups. However, the reality is not the case.
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Less than 20% of Hong Kong elderly population vaccinated
The current coverage rate of elderly homes in Hong Kong is less than 20%, and only about 10% of the population aged 80 or above receive the first dose of the vaccine, and there are still about 10% of the population under 12 years of age who still have not received the vaccine. There are opportunities to be vaccinated. Therefore, the current situation in Hong Kong cannot be compared with Singapore.
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Singapore elderly vaccination rate is about 90%
The overall vaccination rate in Singapore is about 80%, and the vaccination rate for the elderly reaches about 90%.
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Why Hong Kong needs to maintain containment and zero-clearance strategy
However, the immunization rate of the elderly in Hong Kong is low, and the overall fully vaccinated population is only about 45%. Hong Kong has a dense population. Based on past experience, all four waves of epidemics in Hong Kong were caused by imported cases. As long as one case slips through, a large-scale community outbreak can occur in an instant. Therefore, Hong Kong now needs to maintain a containment and zero-clearance strategy, and before considering reopening the border and further relaxing social distancing measures, it is necessary to ensure that all persons who are suitable for vaccination have completed the two doses.
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Clearing the cases and coexistence with the virus, two policy rotation, covid will exist for a long time
Anti-epidemic policies must keep pace with the times and respond flexibly to the various stages of the pandemic with different countermeasures. Therefore, "containment and clearance" and "coexistence with the virus" are not contradictory. COVID-19 will not disappear completely after several months of raging like SARS in 2003. On the contrary, it will be like other human coronaviruses (such as OC43, 229E, NL63, HKU1, etc.), after reaching the balance of herd immunity, it will coexist harmoniously with humans for a long time (see attached table, note 8).
Generally, the human body has some neutralizing antibodies against the above-mentioned human coronaviruses but the immune system cannot completely prevent the virus from infecting the upper respiratory tract. Especially when the antibody level in the body declines over time, such as natural infection after one to two years, the infection can be repeated, and the disease is generally mild (Note 9). However, human coronaviruses can also cause severe illness. For example, the death rate can reach 10% when HKU1 infects the elderly or those whose immune system is suppressed (Note 10).
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Difficult to eradicate any human coronavirus
It is very difficult to completely eradicate the human coronavirus because healthy people have mild symptoms after infection, the source cannot be traced, the spread cannot be stopped, and it spreads to the community in an instant. The new crown is the same. When most people are vaccinated or have natural immunity, the new crown virus is very likely to become another common cold virus. When the level of neutralizing antibodies in the serum declines over time, the elderly and immunosuppressed patients may need to be vaccinated again to enhance immune protection.
The novel coronavirus vaccine was developed and approved for emergency use in less than one year. Therefore, it is absolutely understandable that some citizens are worried and hesitant about the safety of the vaccine. So far, there is no direct cause and effect relationship between serious events after the vaccine, and known potentially fatal complications such as anaphylactic shock (1-2 per million) and myocarditis (50 per million) are extremely rare. Compared with the 2% mortality rate of coronavirus disease, the above risks are insignificant.
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Hong Kong study: Correct use of traditional intramuscular injection can reduce the risk of myocarditis
Recently, our department's research has solved the cause of myocarditis after mRNA vaccine. Only the correct use of traditional intramuscular injection can reduce the risk of myocarditis caused by accidentally injecting mRNA vaccine into a vein (Note 11). As for whether to use the third booster, the clinical trial data is not yet sufficient, and we can only wait for new research data before making a decision.
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Hong Kong predicts the epidemic under control in December 2021
The academia originally estimated that in December this year, the epidemic should be under control, but the emergence of Covi72 has necessitated the re-estimation and planning of anti-epidemic countermeasures by health departments and academia around the world.
Everyone must understand that virus mutation is the law of nature, and whether it mutates or not, human factors cannot control it.
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First-generation covi vaccines are imperfect
In general, the emergence of mutant viruses shows that the first-generation vaccines are not yet perfect, and it has also shattered the illusion of herd immunity. Scientists can only challenge the virus calmly, adapt to current conditions, and with humility, continue to patiently use scientific methods to gradually dismantle this century's problems.
Vaccines are the most tangible and best weapon at this stage to end this century's epidemic. People are urged to cherish the achievements of modern science, seize the opportunity, and get vaccinated as soon as possible.
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Hong Kong experts suggest measures to reduce the risk of Delta infection
Due to the impossibility of border control and the limited effectiveness of the vaccine against the Delta variant, the following measures can be taken to reduce the risk:
(1) Entry persons who have completed vaccination and are positive for serum antibodies can be tested for viral nucleic acid every other day as a condition for relaxing the quarantine period in the quarantine center.
(2) Participating in large-scale gatherings or activities that remove masks, such as banquets, fitness, indoor ball games, singing and dancing gatherings, face-to-face classrooms in middle schools, and other indoor activities, must present a vaccination certificate, and the vaccination rate threshold depends on the epidemic situation. Live fine-tuning. If a newer and more contagious variant virus appears again, face-to-face classrooms must be reduced, and a mixed online (unvaccinated students) and face-to-face teaching mode (inoculated students) should be adopted to reduce the risk of outbreaks in schools.
(3) Strengthen the flow of fresh air in all indoor places, especially schools, banquet halls, fitness rooms, indoor sports fields, private clubs and entertainment venues, such as mahjong halls, karaoke, etc. When investigating at the outbreak site earlier, the Electrical and Mechanical Services Department's measurements showed that the air flow rate in hotels and restaurants was lower than the original design standard. Therefore, it is necessary to ensure that the ventilation system is well maintained.
(4) Vaccines can greatly reduce the lethality of the virus, but cannot completely prevent the spread. Even if 90% of the population is vaccinated, citizens still have to wear masks daily to reduce the chance of transmission. Masks can not only prevent the new coronavirus, but also prevent the spread of influenza and other respiratory viruses. After the extensive use of masks by the people of Hong Kong in the past two years, the seasonal flu has been greatly reduced. At the same time, the immunity of the people against flu will generally decline. Therefore, they must be vaccinated against seasonal flu to prevent a rebound.
The vaccination will be completed by all the people in the next day, and then the coexistence policy can be discussed in depth. However, the vaccination rate is low, and it is difficult to discuss the next stage of epidemic prevention strategies in detail.
Note 1: WHO Coronavirus (COVID-19) Dashboard. covid19.who.int/table. Accessed on 23rd August, 2021
Note 2: Fine P, Eames K, Heymann DL. "Herd immunity": a rough guide. Clin Infect Dis. 2011 Apr 1;52(7):911-6. doi: 10.1093/cid/cir007. PMID: 21427399.
Note 3: Burki TK. Lifting of COVID-19 restrictions in the UK and the Delta variant. Lancet Respir Med. 2021 Aug;9(8):e85. doi: 10.1016/S2213-2600(21)00328-3. Epub 2021 Jul 12. PMID: 34265238; PMCID: PMC8275031.
Note 4: Corbett KS, Flynn B, Foulds KE, et al. Evaluation of the mRNA-1273 Vaccine against SARS-CoV-2 in Nonhuman Primates. N Engl J Med. 2020 Oct 15;383(16):1544-1555. doi: 10.1056/NEJMoa2024671. Epub 2020 Jul 28. PMID: 32722908; PMCID: PMC7449230.
Note 5: Brown CM, Vostok J, Johnson H, et al. Outbreak of SARS-CoV-2 Infections, Including COVID-19 Vaccine Breakthrough Infections, Associated with Large Public Gatherings-Barnstable County, Massachusetts, July 2021. MMWR Morb Mortal Wkly Rep. 2021 Aug 6;70(31):1059-1062. doi: 10.15585/mmwr.mm7031e2. PMID: 34351882.
Note 6: Po Ying Chia, Sean Wei Xiang Ong, Calvin J Chiew, et al. Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study. medRxiv 2021.07.28.21261295; doi: doi.org/10.1101/2021.07.28.21261295
Note 7: Israel, Once the Model for Beating Covid, Faces New Surge of Infections. The New York Times. nyti.ms/3sIW21H. Accessed on 23rd August, 2021
Note 8: Ye ZW, Yuan S, Yuen KS, et al. Zoonotic origins of human coronaviruses. Int J Biol Sci. 2020 Mar 15;16(10):1686-1697. doi: 10.7150/ijbs.45472. PMID: 32226286; PMCID: PMC7098031.
Note 9: Edridge AWD, Kaczorowska J, Hoste ACR, et al. Seasonal coronavirus protective immunity is short-lasting. Nat Med. 2020 Nov;26(11):1691-1693. doi: 10.1038/s41591-020-1083-1 . Epub 2020 Sep 14. PMID: 32929268.
Note 10: Woo PC, Lau SKP, Tsoi HW, et al. Clinical and molecular epidemiological features of coronavirus HKU1-associated community-acquired pneumonia. J Infect Dis. 2005 Dec 1;192(11):1898-907. doi: 10.1086 /497151. Epub 2005 Oct 20. PMID: 16267760; PMCID: PMC7110183.
Note 11: Li C, Chen Y, Zhao Y, et al. Intravenous injection of COVID-19 mRNA vaccine can induce acute myopericarditis in mouse model. Clinical Infectious Diseases, 2021;, ciab707, doi: doi.org/10.1093/cid/ ciab707
The author Long Zhenbang is the Honorary Assistant Professor of the Department of Microbiology, Li Ka Shing School of Medicine, The University of Hong Kong, Zhao Xiyang is the Honorary Lecturer of the Department of Microbiology, Li Ka Shing School of Medicine, The University of Hong Kong, and Yuen Guoyong is the Chair Professor of the Department of Microbiology, Li Ka Shing School of Medicine, The University of Hong Kong.
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