But it is too early to conclude on the death rate and infectivity of COVID-19 as its transmission is still unpredictable, say Professor Paul Ananth Tambyah and Dr Jyoti Somani.
By Paul Tambyah
By Jyoti Somani
SINGAPORE: The novel coronavirus, which the International Committee on Taxonomy of Viruses (ICTV) now calls SARS-CoV-2 as of Feb 11, causes the disease COVID-19. The World Health Organization announced the name of this new disease on the same day.
The virus SARS-CoV-2 is from the same family as SARS (Severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome).
NOT AS DEADLY AS SARS?
It is still too early to tell what is the actual death rate associated with the COVID-19. Many of the people newly infected with the virus are still in hospital or intensive care units so we will not know their outcomes until much later.
For the record, the earliest reports of SARS in leading medical journals cited a death rate of 2 per cent, which later turned out to be higher. It is also not easy to compare SARS and COVID-19 as we did not have a confirmatory lab test until late in the SARS outbreak.
As a result, most of the cases identified globally in March and April 2003, which was about four to six months after the disease first broke, were severe ones, which made the death rate appear higher than it actually was.
In fact, when the SARS test became widely available in Singapore in May 2003, a number of patients were re-classified based on the results of the laboratory tests. As a result, the death rate for SARS in Singapore dropped from 33 out of 200 or 16.5 per cent to 33 out of 240 or 13.8 per cent.
Worldwide, the final death rate was 9.6 per cent.
In contrast, we had accurate diagnostic tests for COVID-19 very early in the outbreak so many individuals with milder diseases have been identified. They would not have been detected if the criteria used were based on clinical severity.
In contrast to both SARS and COVID-19, influenza rarely causes death directly. Severe influenza can cause pneumonia or brain infections but these tend to be rare and in people who have weak immune systems. Influenza mainly causes death by worsening underlying heart or lung problems in older people.
In temperate countries, influenza typically causes seasonal outbreaks during the winter seasons, and outbreaks tend to be worse when there is a shift or major change in the type of influenza circulating that year.
We do not know about the seasonality of COVID-19 yet but SARS disappeared with the warm weather in China and we hope that this will be the case with COVID-19. So, even if COVID-19 returns next year, many people will have some immunity to it and so, we expect that it will not be so bad.
RATES OF TRANSMISSION VERY VARIABLE
Just like the death rates, the infectivity of the COVID-19 virus is still not known.
So far we can observe that while it has spread rapidly in certain settings, there have not been documented transmissions in other circumstances.
In that sense, it is closer to SARS, with occasional “super spreading events” such as in the example of the Amoy Gardens in Hong Kong for SARS, where 329 residents of the estate had been infected with 42 of them dying, and the Princess Dream cruise ship for COVID-19, as well as the very recent large church related outbreak in South Korea.
On the other hand though, except for these cases, the rates of transmission appear to be relatively low with most clusters in Singapore and other settings involving fewer than 10 people.
This is different from influenza, which tends to spread rapidly especially if there is a new strain with a high attack rate – meaning that many people in one setting such as a family or office will be infected when one person is infected.
Part of the reason that Influenza spreads so fast is that it is infectious usually one day, and sometimes two days, before full-blown symptoms manifest themselves.
Similarly, COVID-19 has reports of transmission before the onset of symptoms. There is some early evidence with COVID-19 that the viral shedding from the throat and nose is higher and occurs very early in the infection and then decreases over time.
This is different from asymptomatic transmission of Hepatitis B or C for example. For the Hepatitis B and C viruses, people can be truly asymptomatic for months and years but still spread the virus to their sexual partners or through shared injections.
In contrast, according to reports, most COVID-19 patients who are infectious when asymptomatic go on to show symptoms within a few days, just like patients with influenza.
KIDS AND HEALTHCARE WORKERS
There are however two groups of people who have been affected differently by the virus. The first is children who may not be as vulnerable to the disease as adults.
Both SARS and MERS did not infect many children. They also tended to have much milder symptoms when infected. Influenza also causes mild infection in children, as does COVID-19.
However, children with influenza tend to shed more virus and for longer, thus often making the adults around them sick. We do not know if we will see children with minimal symptoms who still shed the virus with COVID-19.
Another difference between influenza, SARS and COVID-19 is the impact on healthcare workers. While there is a common belief that unvaccinated healthcare workers aided in the spread of influenza among patients, especially in nursing homes, there are no reports of healthcare-associated influenza causing severe disease and death among healthcare workers.
Unfortunately, healthcare worker infections and deaths have been a feature of SARS and have also appeared during COVID-19. In Singapore, however, we are well-prepared with the lessons learned from SARS, so healthcare workers are well-protected this time round.
STRATEGIES FOR DEALING WITH COVID-19
With the novel H1N1 2009 influenza pandemic, Singapore and many other countries initially adopted a containment approach by isolating all infected individuals (initially travellers from the Americas) and quarantining their contacts.
This was followed soon after by a mitigation strategy when the numbers got too high for this to practically continue.
In mitigation, the sickest patients were identified for treatment and isolation and efforts were focused on preventing infection of the vulnerable population.
At the same time, monitoring of cases and surveillance of select populations such as healthcare workers or certain schools allowed us to keep an eye on the pace of the epidemic and make sure that disruptions to normal activities for the population were minimised.
As the WHO has pointed out, COVID-19 will just be a mild illness for most people – for about 80 per cent, just like with SARS. For influenza, the proportion with severe illness is even lower.
The key will be to identify the 15 to 20 per cent of people infected with COVID-19 who are likely to develop complications as we did with SARS.
If we are successful in doing that, regardless of whether we use containment or mitigation as strategies, we will be well-placed to keep ourselves and our nation healthy by the time the epidemic is over with the onset of warmer weather in the northern hemisphere summer as predicted earlier.
Assistant Professor Jyoti Somani, Department of Medicine, Yong Loo Lin School of Medicine, NUS and Professor Paul Ananth Tambyah, Department of Medicine, Yong Loo Lin School of Medicine, NUS and President, Asia Pacific Society of Clinical Microbiology and Infection.