The Covid-19 Chronicles: Risks and hidden things

Glancing through some happy Hari Raya Aidilfitri 2020 photos being shared online, it is difficult to reconcile the fact that we just experienced a Ramadan under the movement control order (MCO); that a globally disruptive pandemic still rages on. But these are details photos often miss.

Similarly, a series of internal events may be unfolding within a person that their outward appearance may never convey. One of the biggest challenges in containing Covid-19, as we move from the phase of lockdown into a phase of living with Covid-19, is the effort required to quickly identify infected people to isolate them from others and prevent further spread.

Unfortunately, unlike its cousin SARS, which is only contagious after people show symptoms of illness, Covid-19 can be spread even before visible clues of the virus within appear.

Unlike SARS, which can be contained by diagnosing symptomatic people seeking care, Covid-19 requires active effort to find patients before they even feel ill. Thus, targeted screening of apparently healthy individuals, at higher risk of being infected or infecting others, is now being conducted in Malaysia and other countries restarting their socioeconomic sectors.

Footballer Adrian Mariappa, most recently of Watford, was shocked when he tested positive during a Covid-19 screening, despite not showing symptoms and following strict social distancing.

But the UK currently records 272,826 confirmed cases, with these numbers being the tip of the iceberg, and the true size of the iceberg of undiagnosed cases depending on the diagnostic capacity of the health system.

Soberingly, public health measures can reduce the risk of getting infected or spreading the disease, but they are not bulletproof. Once the disease is rampant in the community, the risk of Covid-19 increases for everyone—even those taking strict precautions.

But why do some like Mariappa show no symptoms? Why do others face severe symptoms to the brink of death? Malaysia currently hospitalises all Covid-19 patients. But as we continue to live with Covid-19 as we do with dengue, addressing these questions helps us identify those at higher risk of severe illness who should be prioritised for care.

Indeed, dengue is already rearing its head again in the region as we enter the rainy season—and in the backdrop of Covid-19, adds to the list of causes of fever illnesses requiring medical attention.

To address some of these questions, we must first appreciate the Covid-19 risk, that is the threat of becoming sick with Covid-19 and the probability of this actually occurring. Before encountering the risk of disease, one first encounters the risk of infection.

The risk of infection (which for simplicity is assumed to equal transmission) lies in:

1) the biological properties of Covid-19, which are the 10 to 20 times higher ability of SARS-CoV-2 to enter cells compared to SARS and its ability to do so through droplets, persisting aerosols and even contaminated objects; and

2) the properties of the population, such as demographics, behaviour, household size, and natural and built environments.

While it is difficult to assess individual risk of infection, preventive measures such as avoiding close contact or crowding in confined spaces and reducing spread via air and objects through good hygiene and ventilation, collectively adopted by all reduces risk for all.

Once infected, the risk of disease lies in the interplay between the virus and the individual. Unlike bacteria, which can keep multiplying unchecked until treated with antibiotics, viruses can only make more copies of themselves inside host cells.

It is quite common for viral infections to cause sharp sudden damage, then quickly be dealt with by the immune system, receding without treatment. Often, the fleeting viral presence does not produce enough damage or inflammation to garner noticeable symptoms — just a brief cough, or a little scratch in the throat.

However, irregularities in the responses of the body's defenses as is often seen in ageing, and the propensity for self-damaging overreactions when the immune system is already stimulated in chronic conditions such as diabetes have warranted the elderly and those with existing illnesses as groups at risk of developing severe disease when infected with Covid-19.

Despite this, not all elderly infected with Covid-19 will get severe symptoms, and some otherwise healthy young adults may still succumb.

As more people get infected with Covid-19, rare outcomes such as toxic shock syndrome in children, late-term miscarriages, and strokes in young adults are now being reported.

Underlying all this is the fact that while some groups of people share similar characteristics that either makes them more likely to be sick or resist getting sick, the host as an individual is unique and complex, and the roles played by cells of the immune system are far reaching and at times even paradoxical.

Additionally, studies suggest the SARS-CoV-2 persists longer in the body, and suppresses effective early immune responses, while provoking overreactive responses like harmful flare-ups involving multiple immune molecules.

Emerging evidence suggests sunlight and vitamin D may enhance protective immunity in Covid-19, decreasing disease severity — but we do not fully understand how these factors influence the immune processes.

Understanding the interactions of the virus and the immune system on the molecular level will give us a better idea of how the scales are tipped from protective immune responses to damaging immune responses — why some unknowingly clear silent infections, and others require urgent medical care.

Identifying these key markers involved in these different immune responses will enable us to build tools to measure them, and to better distinguish who requires hospitalisation, and who can recover under home quarantine.

Perhaps just as the platelet count is used to assess risk of developing dengue shock syndrome, key Covid-19 markers may tell us what superficial symptoms cannot.

Perhaps a more discerning eye peering through those Hari Raya images might be able to identify the subtle clues. Missing grandparents, the absent open-house reunions, the lack of big family photos with children running around.

These markers of an historic and unusually risky Hari Raya cannot be hidden by the wide smiles in glossy photos.

Keywords: Covid-19, Markers, Response, Immune System, Dengue