By Professor Leo Yee Sin, Executive Director, National Centre for Infectious Diseases; Adjunct Associate Professor Matthias Toh, Director, National Public Health and Epidemiology Unit, National Centre for Infectious Diseases; and Associate Professor Raymond Lin, Director, National Public Health Laboratory, National Centre for Infectious Diseases
It has been 21 months since the first COVID-19 case was detected in Singapore. What have we learned about the SARS-CoV-2 virus that causes the novel disease COVID-19? Similar to the seasonal coronavirus, SARS-CoV-2 infects humans through the angiotensin-converting enzyme 2 (ACE2) receptor that is expressed in the respiratory tract. First discovered in the 1960s, the seasonal coronavirus is believed to be of animal origin and could have been infecting humans for centuries. How it evolved to where it is today remains a subject for scientific research. Today the four known human seasonal coronaviruses cause mild upper respiratory tract infection. Only time will tell whether SARS-CoV-2 will follow suit and if so, how long will it take to reach that stage.
Singapore set a target to end the SARS-CoV-2 pandemic when our vaccine coverage reaches 80% of the entire population and we achieved this by August 2021. However, we are observing an incessant surge in the number of COVID-19 cases even though border control and safe management measures are in place. Is this high number of cases an expected norm as we transit to an “endemic” state?
“Endemicity” in epidemiological language implies there is a baseline number of infections in a population within a geographical area without external importation. The short history of SARS-CoV-2 has yet to establish a baseline level. What else can we do to reduce the viral transmission and impact of the virus on all strata of society?
The strategies to live with SARS-CoV-2
Admittedly, without fully understanding the unpredictable nature of SARS-CoV-2, it is too premature to determine the outlook no matter how eagerly we want to. The strategies ahead include maintaining an open attitude to track and research deeply about the virus, galvanizing support from the masses with clear messaging, making risk-calibrated steps together based on near-term prediction, claiming victory for every milestone and adjusting our steps along the way.
The availability of a vaccine at an unprecedented speed was a huge human achievement. SARS-CoV-2, like any living organism, strives to survive under pressure and we have to expect that change will be a constant. The Delta variant has not only survived but has proven to be fitter and stronger. The vaccine booster is our next strategy to strengthen our defence and it is not unforeseeable that we might have to rely on repeated dosing of vaccine to sustain a high level of immune defence similar to the annual influenza vaccination. We celebrate other milestones like the rapid establishment of treatment protocols primarily with anti-inflammatories such as steroids, immunomodulators such as the JAK and IL-6 inhibitors, and antivirals such as remdesivir which can hasten time to recovery. Promising new antiviral agents together with modalities such as monoclonal antibodies provide opportunity to intervene at earlier stages of the disease.
Speed and agility are vital to keep pace with the rapid evolution of SARS-CoV-2. We have learned that the majority of cases had mild illnesses except those unvaccinated and seniors with weakened organs from multiple chronic illnesses. The strategy to cope with the large number of cases is to rapidly re-organise our care model, establish a triage system to allow milder (lower risk) cases to recover at home, provide adequate knowledge and information to self-care, shift the reliance from hospital to community, and preserve acute hospital beds for those with serious illnesses that require active medical intervention. We need to reorganise manpower resources to strengthen higher acuity care in hospitals where more cases require supplementary oxygen.
Ensuring all segments of the population are protected from SARS-CoV-2
How SARS-CoV-2 will evolve and change its biological characteristics cannot be accurately predicted at present. However, we are clear that the Delta strain is highly efficient in transmission regardless of vaccination status, evades innate and adaptive immunity leading to increasing number of vaccine breakthrough cases. Close to one million of our population, including children below 12 years old, are without vaccine protection. Our older population continues to bear the hardest hit, together with those who cannot mount good immune response despite vaccination.
It has been suggested that having an asymptomatic infection post vaccination is the best solution for the younger population to achieve natural immunity. Although this may sound scientifically and mentally palatable, such a proposal may neglect the public health protection of the vulnerable population at two extremes of age – the very young and the very old.
This SARS-CoV-2 virus is highly divisive and has engineered an unequal impact to different segments of the general population. The best strategy for one segment does not necessarily serve another. Now is the time for national unity and to do our best to minimise the risks to the vulnerable groups. We have to take it upon ourselves not to get infected and block the chain of transmission through adherence to safe management measures.
Eradicating SARS-CoV-2 is no longer an attainable goal. Expect on-going COVID-19 cases interspersed with clusters and outbreaks. It is a long winding road ahead of us as we strike a fine balance between considering the needs and demands from many facets of the community while ensuring adequate provision of healthcare for both COVID-19 cases and non-COVID-19 patients.
The article was also
published in Lianhe Zaobao on 2 October 2021.