‘Are we sufficiently prepared for the next viral outbreak? No, not really ...’

Epidemiologist Hans Heesterbeek and virologist Marion Koopmans talk about emerging infectious diseases

LEeg waarschuwingsbord tijdens coronacrisis

For months now, the novel coronavirus SARS-CoV-2 has held the world in its grasp – and the end is not yet in sight. Should we have seen this pandemic coming? While virologists and epidemiologists say there was no way to foresee this specific virus, they have been warning us for years of the threat posed by new viruses with pandemic potential. Will we face outbreaks of this kind again in the future? No doubt about it, according to the experts. And when asked whether we are sufficiently prepared for this, the answer is definite and unanimous: not yet. We spoke with epidemiologist Hans Heesterbeek and virologist Marion Koopmans about the risks of emerging infectious diseases.

‘A pandemic caused by a coronavirus didn't really come as a surprise to us,’ says Marion Koopmans, head of the Virology department at Erasmus MC and scientific director of Emerging Infectious Diseases Preparedness at the Netherlands Centre for One Health (NCOH). She has become a familiar face in the media these days.

‘Coronaviruses have been on the list of potential pandemic threats – a shortlist created by the WHO after the 2014 Ebola outbreak – for quite some time. And coronaviruses are among the ‘Top-10 Blueprint priority diseases’ as well. We knew, in other words, that we had to look out for coronaviruses such as SARS and MERS, because they have can have such a rapid person-to-person transmission rate. Yet the speed with which this particular virus spreads, and the extent of the spread, did manage to surprise us! It happened really fast.’

Marion Koopmans
Marion Koopmans (© Levien Willemse)

Greater threat than before

For decades, experts have been warning us that more and more infections are making the jump from animals to humans. ‘The threat is greater now than in the past thanks to the myriad ways we have organised our world,’ says Hans Heesterbeek, Professor of Theoretical Epidemiology at the Faculty of Veterinary Medicine. Like Koopmans, Heesterbeek features regular in the news. ‘But even so, with a new virus like this one, you have to wait and see which parts make the jump and what the virological, epidemiological and clinical characteristics of that virus will be. With SARS, those characteristics turned out not to be too bad in terms of the potential for transmission, while this novel coronavirus has emerged as a much graver threat. This is primarily due to its early symptomatic, mildly symptomatic and perhaps even asymptomatic infectivity. That makes a virus much more difficult to stop. And you can't know this until the virus has made the jump and adapted itself to a human host.’

‘We must prepare for a future involving more frequent outbreaks of infectious diseases’

The virus goes underground

‘What really sets this particular coronavirus apart is the extremely diverse range of symptoms and the infectivity of people with quite mild signs of illness,’ Koopmans says. ‘We observed these characteristics to a much lesser degree in SARS and MERS. As a result, the virus is manifesting itself very differently. When you have a whole bunch of people with very mild symptoms, it's easy for the virus to go underground, as it were. This has huge consequences for the spread. We are seeing people with mild symptoms who shed plenty of viral particles, and even people who are completely asymptomatic yet still test positive and carry the virus. The debate concerning the significance of the latter group in spreading the virus remains ongoing.’

Hardly any symptoms and yet contagious

Another way this new coronavirus differs from SARS and MERS is that those viruses were found primarily in the lower respiratory tract – in other words, deep in the lungs – and to a much lesser degree in the upper respiratory tract, that is in the nose. This likely explains why SARS was much less contagious. ‘With SARS, the viral shedding also peaked one week after symptoms started, at which point the person was quite ill,’ Koopmans says. ‘This works like a kind of automatic quarantine, because the person stays in bed and limits their social contact. And this then is part of the solution in itself.’ ‘With this coronavirus, however, people are walking around feeling fine while their noses are packed with viral particles. This is obviously a perfect set-up for rapid spread and is very different from the situation we faced with previous coronaviruses.’

Hans Heesterbeek
Hans Heesterbeek

Is this the first coronavirus to become a pandemic in such a short span of time?

‘It's not the first coronavirus to do so, because we already had SARS and MERS,’ Heesterbeek explains. ‘While they may not have reached pandemic status, they did emerge in the same interconnected world where travel was commonplace. The only difference is that those viruses had other characteristics. There's no doubt that we dodged a bullet where SARS is concerned!’

‘Looking at evolutionary studies, there are solid reasons to believe that the vast majority – if not all – of the ordinary coronaviruses that fall under the common winter cold originated in the animal kingdom,’ Koopmans adds. ‘They have a global distribution, so they must have caused pandemics at some point in time. The earliest can be traced to somewhere between 1800 and 1900. While we can never know for sure, it is something to be taken into account when estimating the threat of pandemic posed by coronaviruses.’

‘We really dodged a bullet where SARS is concerned!

Were we prepared for this outbreak?

‘To a certain extent we were, but in many other areas we were not,’ the virologist answers. ‘Within a few weeks, the virus’ genetic code had been shared around the world and the WHO had rolled out diagnostics. That was absolutely the quickest possible response, and it meant that travellers could be screened. A lot of progress has been made with regard to vaccine development as well. While we're able to move faster now, that doesn't mean we will be able to prevent such outbreaks in the future. In terms of interventions, hopefully we will have real options before too long. Europe in particular has invested heavily in this area over the past decade. But if you were to ask whether the Dutch economy is prepared for another rapidly-spreading virus, my answer would have to be no. The capability of our current cooperation is simply outmatched by the speed of transmission and characteristics of this virus.’

Heesterbeek: ‘Knowledge of infection dynamics within my field, epidemiology, has undergone tremendous growth as well. There are a great many things we can calculate using models. But we were unprepared for this pandemic because we'd never seen anything on this scale before. For example: we don't know which measures are most effective, nor can we say how they are disrupting society and the economy. What balance should we strike? The most difficult phase is the one we're facing now – how to reopen society.’

Will there be a second wave?

‘If we return society to the way it was at the start of 2020, there will definitely be a second wave,’ according to Heesterbeek. ‘All the models show us this. If we did that, of course nothing would really have changed: the virus will still be the same and perhaps 90% of the world population would still be vulnerable to infection. Six months ago, we never imagined that something so drastic could occur. So we need to realise that a second wave could very well take place if we do nothing. If we slacken now, a new lockdown is the only thing that will help. The virus certainly won't ease up – it will only benefit from our slackening.’

‘Slackening will mean another lockdown. The virus certainly won't ease up – it will only benefit from our slackening.’

Could another virus strike while we’re busy fighting this one?

‘I don't want to paint that dire a picture,’ says Koopmans. ‘But we also shouldn't assume that the next pandemic will take a century to emerge, like after the Spanish flu of 1918. The world has changed drastically since then. We're more surprised that it took this long to happen. So while we do need to act at a global level, doing so requires a level of worldwide coordination that doesn't exist.’ 

Outbreaks caused by mosquitoes

In addition to outbreaks caused by zoonoses – infections that jump from animals to people – the Netherlands can also expect further outbreaks of infections transmitted by arthropod vectors such as mosquitoes. ‘Especially in light of increases in global trade, passenger travel, land use, our natural areas and climate change. Its vast quantity of water, transport and dense populations of people and livestock make the Netherlands particularly vulnerable to this type of outbreak. To gain a better understanding of whether and how these changes lead to new outbreaks, and to more effectively prepare ourselves, NCOH is hosting the research programme One Health PACT (Predicting Arboviruses Climate Tipping Points).’

‘This research calls for true interdisciplinary collaboration,’ Heesterbeek adds. ‘Shortly before the COVID-19 pandemic began, a group of us led by Marion received a large grant for this purpose from the National Science Agenda (NWA). Ironically enough, the start of the project has itself been affected by a pandemic.’

Are you concerned about new outbreaks?

Koopmans: ‘I think we should be taking the threat of new infectious diseases quite seriously, because you can count on them emerging at some point. We should really be making a structural effort to prepare for new infectious diseases – and that includes the healthcare sector. During the Ebola outbreak in West Africa, all the hospitals suddenly had to practise with the protective measures that need to be taken when dealing with a patient with a fever. It's not good to only start thinking about these things after an outbreak has occurred. We need to embed outbreak preparation in a much more structural way.’ 

This is an article from Vetscience no. 8, July 2020.