The COVID-19 outbreak has gone global, infecting more than 100,000 people in all continents across the world, except Antarctica. In a Channel NewsAsia commentary, the Department of Medicine's Prof Paul Tambyah and Dr Jyoti Somani elaborate on some likely scenarios of how the WHO-declared COVID-19 pandemic will play out.
The World Health Organization (WHO) has now declared this a pandemic to galvanise the world to fight the SARS CoV2 virus which causes COVID-19 disease. This declaration has had a significant economic impact but it will hopefully succeed in mobilising resources to contain the rapid rise in cases seen globally. The WHO has also said that this is the first pandemic to be caused by a coronavirus but it will also be the first pandemic that can be controlled.
Two trajectories the global spread could take
Like SARS, the vast majority of patients with COVID-19 will experience a mild illness. A small proportion, about one in 8 to 10, will require intensive care, and some may not survive. With SARS, testing only became available weeks after the outbreak began, meaning that many mild cases early on were missed, inflating the fatality rate. The other big difference between SARS and COVID-19, especially in countries previously affected by SARS, is the high degree of healthcare worker protection, which may mean lower rates of infections in medical professionals working on the frontlines.
There are two possible scenarios we foresee going forward. In these, it is important to keep in mind that the extent of the global outbreak in the following months will depend on many key factors that can be shaped, including public health responses, the developments in rapid testing, demonstration of effective treatments and potentially the roll-out of a vaccine.
In the first scenario, the epidemic slows down in the northern hemisphere as it starts to warm up. Even now, the countries with high chains of transmission are those where the temperature remains in the 10 to 15 degrees Celsius range and below - South Korea, Italy, Iran and other European countries, as well as the northeast and northwest of the US. While many tropical countries have had some cases, so far, there has not been widespread community transmission so far, perhaps because the higher humidity and warmer weather may be preventing rampant spread. While the virus might disappear altogether in the northern summer like SARS, there is also the risk that, similar to the influenza pandemics of 1918, 1957 and 1968, the COVID-19 outbreak may slow down during the northern hemisphere summer season, but may return in a second wave in October or November when it gets cold again.
The second possible scenario is that the COVID-19 disease may turn out not to be sensitive to temperatures, in which case, the spread of infection will continue worldwide for months, at least until herd immunity develops in communities. Scientists are speculating what proportion of the population will get infected in that case. For H1N1 in 2009, we know that figure was around a quarter of the population after the first wave of infections. We also know that COVID-19 is more severe than influenza so the impact on healthcare systems, especially in low and middle-income countries can be significant if such large proportions of the population are infected.