Source:
https://scmp.com/comment/opinion/article/3101741/how-hong-kong-can-avert-fourth-wave-covid-19-infections
Comment/ Opinion

How Hong Kong can avert a fourth wave of Covid-19 infections

  • Studies show that infection transmission can vary widely depending on the primary setting. An understanding of the different risks involved would help policymakers maintain control even as containment measures are relaxed

In this Covid-19 pandemic, understanding the transmission dynamics of infection is key to controlling it. Following our success in containing the second wave of infections originating from returning Hongkongers, social restrictions were relaxed in stages, but this was followed by another resurgence that reached alarming levels.

Resolute government decisions to impose correspondingly restrictive social-distancing measures have led to a gradual decline in local transmissions, from the peak of 149 cases of infections to single digits. Of greater significance than the number of infections was the incidence of chains of infection across different settings, most notably in bars, restaurants and eateries, markets, workplaces, places of worship, container terminals and homes for the elderly.

Understanding the variability of infection transmission, as inferred from global molecular epidemiological studies, is increasingly recognised as paramount to controlling the pandemic. Mathematical modelling estimated that 10 per cent of Covid-19 cases might have accounted for 80 per cent of transmissions worldwide. Studies in Hong Kong have also found that 20 per cent of cases were responsible for 80 per cent of local transmissions.

In Hong Kong, the largest cluster of 103 cases emerged from a bar-and-band setting. Globally, massive outbreaks have been reported from “superspreading events”, including mass religious gatherings and entertainment and sports events.

Understanding the risks for transmission in these clusters which could lead to large outbreak of infections is critical for maintaining control, as social-distancing measures are relaxed. The viral load or infectivity of the human source is one key determinant of transmission risk. The other is the type of setting in which cluster transmission takes place, which can be controlled.

The variables in the setting are: first, environmental – indoor settings which are crowded and poorly ventilated have the highest risk; second, s ocial – the proximity, duration and type of contact in the setting and; third, behavioural – the extent individuals practise physical distancing, cough etiquette, wearing of face masks, and hand and respiratory hygiene

Research by the Chinese University’s School of Public Health and Primary Care, using network epidemiological analysis of 121 clusters in Hong Kong, found that although households are the most frequent primary setting where infections were first detected and had the highest number of linked cases, transmission was often confined within the household and only infrequently linked to transmission in a different setting.

In contrast, the setting associated with the largest number of 103 cases was in the entertainment industry (bar and band), and was propagated through 31 different secondary (subsequent) settings, spanning 26 days. The entertainment-venue setting, comprising a casual social mix of individuals, was epidemiologically linked to a diverse range of subsequent settings of infection transmission, including households, neighbourhood, eateries, parties, personalised services, the workplace and public transport.

People at a restaurant at Tsim Sha Tsui on September 11. Hong Kong doubled the number of people allowed to gather in public and reopened sports venues that day, in the latest easing of Covid-19 restrictions. Photo: Bloomberg
People at a restaurant at Tsim Sha Tsui on September 11. Hong Kong doubled the number of people allowed to gather in public and reopened sports venues that day, in the latest easing of Covid-19 restrictions. Photo: Bloomberg

The latter setting reflects a propensity for widespread dispersion, difficulties in contact tracing and containment, and the potential for seeding “undetected carriers” in the community. The risks of community spread from these two primary transmission settings are evidently very different.

Network epidemiological analysis of transmission cascades or clusters can be applied as a risk-assessment tool to guide decisions on relaxing social distancing.

Hong Kong must do all it can to avert a fourth wave. But the socio-economic and personal costs associated with containment measures such as social distancing means we must carefully consider the strategy. The relaxation of restrictions in socio-economic activities needs to be staged and planned, based on risk assessment supported by science and informed by the knowledge gained from our own and global experiences.

A comprehensive risk-assessment framework covering border controls and different socio-economic and environmental settings is critical to avert another significant resurgence. This means identifying and, where possible, quantifying the risks associated with the different settings, to mitigate, manage and monitor them. Such efforts should inform policy decisions in targeting social restrictions that minimise the impact on our society and economy.

Many business sectors have instituted measures to mitigate risks. However, a more structured collaboration in risk planning is necessary. We could use the industry-specific risk assessment tools available in the World Health Organisation repository to develop appropriate industry practices. Oversight from the industry itself, using a mix of compliance and deterrence strategies, will help.

A holistic approach would be necessary to mitigate risks for vulnerable populations, and where populations have little or no choice but to live in crowded areas, such as long-term residential care facilities, dormitories and prisons. Pre-testing and segregation is already being implemented in these settings. Reducing the need to seek medical care and hospitalisation would be a more effective preventive strategy for long-term care homes, by enhancing primary geriatric and palliative care.

The public would also need to be convinced of the continuing need for physical distancing, maintaining good hygiene, and compliance with restrictions to socio-economic life which are proportionate to the prevailing transmission risk.

The impact of these restrictions on vulnerable and disadvantaged populations needs to be assessed and mitigated. We should recognise that they have contributed equally to the overall efforts to combat the pandemic but have had to suffer disproportionate costs.

The risk-assessment framework would bolster the city’s surveillance mechanisms, testing strategy and contact-tracing protocols, and enable earlier and more defined interventions to prevent a surge in transmissions.

With the easing of restrictions in the midst of a global pandemic, Hong Kong’s public health surveillance and response system needs to be continuously evaluated to be able to detect transmission risks and pre-empt any resurgence which could be generated from clusters of linked transmissions in high-risk settings.

Hong Kong has the capacity, knowledge and experience to avert a fourth wave of infections and the avoidable social and economic costs.

Yeoh Eng-kiong is Professor of Public Health and director of the Centre for Health Systems and Policy Research, JC School of Public Health and Primary Care, Faculty of Medicine, at the Chinese University of Hong Kong