This article focuses on the information that health authorities have to work with when making decisions about how to contain a viral outbreak like COVID-19.

Working backwards from the worst-case scenario.

The WHO has long been concerned about the possibility of a “Disease X” that could become a serious pandemic. COVID-19 could be Disease X. Since the SARS outbreak of 2002-3, epidemiologists have regularly modelled the projections and outcomes of a hitherto unknown, infectious coronavirus that will come from abroad and spread around the world. Once such model from John Hopkins University involved a model that was simulated in October 2019 where a coronavirus outbreak left 65 million people dead worldwide.

There are two principal reasons why an outbreak of an infectious virus is worrying. Firstly, viruses spread exponentially. Think of the 282 cases of COVID-19 on January 20th to the 80 238 cases today as an illustration of this. The sheer numbers astonish many of us, and we jump to worst-case scenarios: 65 million dead and post-apocalyptic societies. Reporting on government’s plans that outline worst-case scenarios is favourite tactic of tabloid newspapers to sensationalise disease outbreaks and, frankly, to scaremonger.

Secondly, uncertainty in a virus outbreak is common, especially in the early weeks. This means we only have little or patchy data and conflicting information. When a new virus spreads, as COVID-19 currently is across Europe, decisions about how to contain it are based on data that continuously changes. In addition, in this space of the unknown, bad information thrives, the public’s fear rises.

Frequently, in disease outbreaks, epidemiologists and public health experts start from a worst-case scenario and work backwards to pinpoint the situation in reality. This includes identifying the nature of the virus, the spread, who is more at risk of dying from it, what social, demographic and economic impacts the outbreak may have and, above all, what measures need to be taken to contain, to treat, to prevent and to eradicate the virus.

For example, with the Zika outbreak in 2016, the first recorded cases were those who were extremely sick who came for treatment in hospitals. Then, it was noted that pregnant mothers infected with Zika would give birth to birth to brain-damaged babies. In time, milder cases were identified and became part of the total of cases as soon as health workers started identifying people who were infected.

Early projections and estimates often overstate the severity of a new disease. The same may have happened with COVID-19. The first cases that were presented were severely ill, showing symptoms of pneumonia and respiratory failure. Health workers were initially seeing the 20% of people infected with COVID-19 that required hospital treatment and the 2% of cases that died. Then, they were witnessing who other healthcare professionals and family members of the infected were also showing symptoms. Through the fog of uncertainty that is characteristic of a new disease outbreak, health workers in China started seeing milder cases. The nature of COVID-19 was gradually revealing itself to have a lower mortality rate compared to other virus outbreaks: SARS has a 10% mortality rate, MERS, 34%, and Ebola, 50%.

COVID-19: A ‘Known Unknown’

COVID-19 itself is an ‘known unknown’. Known, in the sense that it is a coronavirus, like common cold or the seasonal flu. Unknown in the sense we do not know enough about its true character. I originally compiled the list below of ‘unknowns’ of COVID-19 in early February and it has been interesting to see, over the intervening weeks, how much more we have learned and what remains unclear:

How is COVID-19 passed on?

Health workers are still learning about how COVID-19 is passed on. In the early weeks of the outbreak, it was noticed that large numbers of infected in Wuhan were health care workers and relatives of the sick. This suggested that the virus was transmitted via close contact, rather than casual. Close contact means being within two metres of an infected person for 15 minutes or more.

When and how did the virus jump from bats to humans?

It is believed that bats are the likely reservoir for the virus and then jumped the species barrier, possibly via a third animal, such as a live pangolin illegally traded at the Wuhan seafood market. None of this is yet certain. Neither is when the jump to humans happened: possibly at the end of December 2019, possibly weeks before. It is still an unknown.

Why did some of the first cases reported in Wuhan not have any apparent connection to the Wuhan seafood market?

There was no epidemiological link between the patient and the market that was clear and traceable. Besides, it has been suggested that the virus could have been in circulation in Wuhan for some weeks before cases were being clearly linked to the market. We do not know for sure.

The same goes for cases in Europe, such as the current outbreak in Italy, where no clear epidemiological link has been established between new cases and anyone else infected. The truth is that there is a link, it simply has not been established yet.

How many have been infected? Exactly how many unrecorded cases have there been?

In the early weeks of the outbreak, it was suspected that mild and asymptomatic cases may not have been making into official figures. Therefore, the number of deaths has so far been measured against a smaller base than it should have been. Estimations from within Wuhan suggest that as many as 1.3% of the city’s population may have / have had the virus without knowing it. By extrapolating this figure to include the whole of China, the case numbers could be as many as one million people. With a mortality rate of 2.3%, we could see 23,000 deaths in China alone. So far, this has not been the case.

Eighty per cent of deaths in China and elsewhere have been amongst people aged over-60, typically with pre-existing chronic illnesses, especially diabetes and cardiovascular diseases. If this is the case, then the death rate could be relatively higher in some regions where the median age is higher (EU median age: 43 years; 25.7% of the population is aged over 60), and lower in regions where the median age is lower (Niger media age: 14.9 years; 2.2% of population is aged over 65).

How contagious is COVID-19? Is every case equally infectious? Are some people less likely to spread it while other people are super-spreaders? What about mutation?

COVID-19 may be spread in a similar way to MERS and SARS, by droplets, fomites and close contact. Depending on which study you read, the transmission rate of COVID-19 is estimated between 1.4 and 4.0 – a large margin of difference. Going from the spike in cases in Italy today (a 25% surge in 24 hours), COVID-19 is possibly more contagious than initially thought; the higher number of 4.0 may be more accurate.

Viruses do not spread in a linear manner, going from one person to another until a large number of people has been exposed and infected. Super-spreading events occurred with other coronavirus outbreaks, such as, in South Korea in 2015, where one person infected with MERS spread it to over 80 people during a single stay in hospital. Likewise, we have seen that COVID-19 has its super-spreaders too. We have seen instances where infected people with unusually high viral loads, have infected multiple people. This has occurred in the UK, South Korea, Iran and Italy. As regards mutation, all evidence points to the virus remaining stable, showing no signs of mutation or increased virulence.

Will it become a global disease?

We already know that it is already going global. Reviewing press articles from late January, it was hoped that the global spread would be months away. A pandemic in late spring in the northern hemisphere would mean that hospitals would be over the flu peak, be in a better position to deal with a surge of COVID-19 cases, and advances would be made in the development of treatment and vaccines. However, we are witnessing the global spread of the virus now. This brings into question China’s tactics of lockdown and quarantine of Hubei province and Wuhan in particular. Has containment worked or was it too late? We will only be able to answer that question in hindsight.

Will it be seasonal? Will the progression of the virus change or become weaker with the changing seasons?

In early February, the Cambodian Minister for Health, Mam Bum Heng, was rebuked by the country’s Prime Minister for claiming that COVID-19 will not be able to thrive in Cambodia’s hot climate, given that the virus cannot survive in temperatures higher than 30°C. On February 10th, Donald Trump stated that the virus will probably die off in the spring months, owing to rising temperatures. This view was also suggested by Matt Hancock, UK Health Secretary, last week.

The reality is that we do not know if this will be the case. MERS, for example, first spread in the Saudi Arabian August, when average temperatures reach 42.8°C. One theory is that it could burn itself out during the summer in the northern hemisphere and return as winter draws in. Alternatively, it could cross over into the southern hemisphere, as it has done in Brazil this week, and spread faster during the southern winter months and cross back over to the north in time for a fall in temperatures.

Filling knowledge gaps about a new infectious disease is a gradual, ongoing process and one that constantly changes in the light of new evidence. This is a key part in combatting an outbreak. The more that is known about the ‘unknown’ elements of the virus enables countries and their populations to be better prepared.

The next article focuses on possible trajectories and outcomes of the COVID-19 virus.

By Mark Gibson, Health Communication Specialist, 26th February 2020.

References:

Coronavirus cases surge to 400 in Italy, BBC News, 26th February 2020 [ https://www.bbc.co.uk/news/world-europe-51645902 ]
Coronavirus: How bad will it get?, The Economist, February 1st 2020
Kucharsky A, Misinformation on the coronavirus might be the most contagious thing about it, The Guardian, 8th February 2020
Le Page M, Will heat kill the coronavirus?, New Scientist, 22nd February 2020
MacKenzie D, How bad is the COVID-19 coronavirus outbreak likely to get?, New Scientist, 11th February 2020
Park A, Campbell C, Containing a crisis, TIME, February 10th 2020
Prepare for the worst, hope for the best, The Economist, February 1st 2020
Savi K, Cambodia too hot for virus, The Phnom Penh Post, 29 January 2020
Time and again, The Economist, January 25th 2020

COVID-19: collapsing societies, mountains of dead. Working backwards from the worst-case scenario.