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COVID-19 Update

It has been a few weeks since our last update. Having achieved a degree of normality in Hong Kong, the recent increase in cases has brought further social distancing measures. As we have described throughout this process, Hong Kong has world-class expertise and systems in the management of infectious disease. This explains the excellent management of the epidemic within our city.

Research from the University of Hong Kong (HKU) showed that 20% of all cases of SARS-COV-2 infection in Hong Kong were responsible for 80% of subsequent infections. The phenomenon of super spreading events has been recognised internationally. As an example, the Lan Kwai Fong bar cluster was responsible for 73 primary cases and was ultimately responsible for 106 total infections which represented 10.2% of total cases and 30.4% of local cases at that time. The study showed the risk of infection to be significantly higher in social exposure in comparison to family or work exposure. This supports similar findings internationally. The School of Public Health have developed a weighted model, integrating big data and health data, to measure the real-time effective R0 in Hong Kong. This allows public health strategies to be modified on the basis of evolving evidence. This is the reason that recent social distancing measures target a reduction in higher risk social exposure. One simple way of considering risk in this context is that risk increases significantly when you are “breathing somebody else’s air”. Infections do occur in lower-risk situations but the probability of infection and of super spreading events increases as groups gather in close proximity. Instinct may suggest that it is illogical to close restaurants in the evening and not at lunchtime. However, people spend less time in restaurants at lunchtime, are more compliant with mask use and drink less alcohol. Evenings are associated with an increase in alcohol consumption, social interaction and group gatherings, which increases the risks of super spreading events. The goal of social distancing interventions is to nudge changes that bring cases under control whilst minimising disruption to normal life. This is a new and evolving epidemic, lessons from different strategies will facilitate evidence-based responses as the level of community infections ebb and flow within Hong Kong.

We are very grateful for the number of people who volunteered for the serology study which we undertook in association with the School of Public Health at the University of Hong Kong. The study has not yet been published but has revealed a number of interesting results. The overall seroprevalence in the OT&P population was 1%. Whilst this initially seems very low, it compares to zero in a study of over 3,000 local blood donors. The majority of cases, unsurprisingly, were imported. We saw no statistical difference in the incidence in children and adolescents. In fact, the data supported our early hypothesis that young people are spreading this infection but not suffering the serious consequences. We did see evidence of cases being transmitted whilst in home quarantine, in addition to an expected increase in cases in individuals who returned to Hong Kong later in the study period. Both factors would suggest that the introduction of public health controls, in particular quarantine, was a factor in reducing the number of cases in Hong Kong. In addition to a selection of our patients, we also tested blood samples on 121 pilots and aircrew as well as 89 members of OT&P staff. The incidence in aircrew was no different to that of our patient population. We saw no evidence of occupational infection in any member of our medical staff despite remaining fully functional and conducting more than 3,000 COVID-19 tests over this time.

The University of Hong Kong is a world-renowned centre for coronavirus research. The samples in the OT&P study have been tested by a variety of methods, including for the presence of neutralising antibodies. We have shown that a small proportion of proven infections either do not produce, or quickly lose, neutralising antibodies. In addition to looking at antibody testing we are involved in a further study to analyse the T-cell response of individuals who are known to have been infected. The role of T-cells in the immunity of COVID-19 will be an important factor in the evolution of the epidemic. We know that in SARS and MERS, T-cell immunity was more effective and longer lasting than the B cell antibody response. There is some early suggestion that T-cell immunity will be important in COVID-19. Ultimately this study will contribute to the understanding of optimal testing for serology which by definition has an impact on understanding infection and mortality rates associated with the SARS-COV-2 virus.

There has been increasing understanding over the last few weeks of the impact of genetic mutations on infectivity. There is good evidence that a mutation (D614G) rapidly became the most common sub-type in Europe and subsequently the seeding to North America and the recent outbreaks in Beijing and Hong Kong. This mutation appears to confer higher infectivity. Similar findings have been confirmed by our colleagues at the University of Hong Kong in a study that is yet to be published. As we have explained previously there tends to be an inverse relationship between infectivity and severity. This virus is likely to spread more widely but with no increase in clinical severity. We have explained previously the dilemma of predicting mortality rates in evolving epidemics. A recent meta-analysis from Stanford University suggested a corrected infection fatality rate for COVID-19 of 0.02 - 0.4%.

There has been talk recently about second and third waves in Hong Kong. In reality the world is currently in the first wave of COVID-19 and Hong Kong is in the third ripple of the first wave. There are many uncertainties as to what will happen next. We can think of possibilities along a spectrum. One view is that current antibody levels suggest still small numbers infected, well below the traditional thresholds for herd immunity. In this scenario, until we get a vaccine the world will need to, at least intermittently, employ social distancing measures to prevent more serious second and third waves. In this model, the pandemic is likely to have a significant impact over a number of years. An alternative, more optimistic potential scenario, would suggest that in some regions a significant percentage of the population already has immunity, not only from antibodies but also from T-cell responses, either relating to this infection or previous infections. In this scenario, we are much closer in some populations to herd immunity. This model would suggest a very infectious illness but one with a relatively low fatality rate in the vast majority of cases. In this situation, the epidemic may be expected to either burn through and die, or remain with episodic clusters. The two scenarios above represent a simplification of a spectrum of reasonable possibilities. In either scenario, the obvious infectivity of SARS-COV-2, makes it extremely unlikely that Hong Kong could completely eliminate the virus without unacceptable social and economic harm. As we have previously explained, management of infectious disease is a balance between the cost of the disease in human terms and the social, political and economic impact of the public health measures. As we develop a greater understanding of the immunology of the disease, in addition to the evolving epidemiology in regions with different public health strategies, we will understand better the numbers of vulnerable individuals in different communities and the true risk of the threat to those individuals. This will allow more balanced decisions regarding public health regulations versus a focus on restoring economic activity. We are fortunate to have world-class systems and expertise in the management of infectious disease. The challenge will be to control the epidemic, to protect both the health system and vulnerable members of the community, whilst minimising disruption to normal life.

COVID-19 has been a significant Black Swan event. There is still a significant amount of rapidly evolving information about this new disease. Communicating risk in evolving epidemics involves recognising uncertainties and being prepared to change advice on the basis of evolving evidence. Early in this process, we underestimated the infectivity of this disease based on data from the early clusters. We could arguably have been quicker to explain the evolving evidence for face masks in reducing community spread. Whilst we were not alone in either situation, it is important to appreciate that bias from previous experience can be important when dealing with new illnesses. It is important to learn the lessons from the past but also to recognise the specific variables and uncertainties of the present. Education, reliable information and effective communication remain key factors in the management of epidemics of infectious disease. We have put copies of all our newsletters and blogs on our website as a historical record of this evolving process.

There has never been a better time to reflect and recognise the essential workers who make our city tick. Workers in energy, transport and essential services, cleaners, drivers and all those working in frontline roles. We would also like to explicitly acknowledge our thanks and gratitude to all OT&P staff, especially our nursing, reception and support staff who have been working longer hours than usual often in challenging and uncertain circumstances.

All our articles are available in Chinese HERE.

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