We need to prepare for an Ebola pandemic that spreads like the measles

By Martin Michaelis and Mark Wass. If we want to be prepared for future pandemics, we need to be prepared for the worst case scenario.

In the light of the ongoing COVID-19 pandemic, world leaders have called for a global plan to deal with further pandemics in an internationally coordinated way. They argue that the question is not “if” another pandemic is going to happen but “when”.

Prior to this pandemic, many thought that devastating infectious disease outbreaks were a thing of the past due to scientific progress and improved surveillance systems.

However, the COVID-19 pandemic has shown us how vulnerable we still are. COVID-19 has caused the worst pandemic since the Spanish Flu in 1918-1920 and the greatest devastation since the Second World War. Without lockdowns and restrictions at an unprecedented scale, the COVID-19 pandemic may easily have already reached the lower end of the death toll estimations of the Spanish Flu.

Despite the massive devastation that COVID-19 has caused, it is not a particularly virulent disease. Future pandemics may be much worse. The infection-fatality-rate for COVID-19 (the percentage of infected people who die) is estimated to be between 0.5% and 1.5%. Ebola virus disease death rates range from 30% to 80%. The Middle East respiratory syndrome (MERS) has so far killed 882 (34.4%) out of 2,566 infected individuals. It is caused by the Middle East respiratory syndrome-related coronavirus (MERS-CoV), a coronavirus that is related to SARS-CoV-2, the coronavirus that causes COVID-19. There are also many highly pathogenic avian influenza (bird flu) viruses that cause mortality rates of up to 60% in humans.

The difference between these viruses and SARS-CoV-2 is that they are not readily transmitted between humans and, in particular, that there is no asymptomatic transmission. The SARS outbreak in 2002/2003 was caused by the coronavirus SARS-CoV, a close relative of SARS-CoV-2. SARS was quickly stopped, because SARS patients were only infectious when they displayed symptoms. Hence, carriers were easy to identify and isolate. In contrast, many SARS-CoV-2 infection chains go unnoticed without testing, because those who transmit the virus are unaware of their infection.

Given the massive devastation that COVID-19 has caused, it is easy to imagine, the catastrophe that could be caused by a deadlier pandemic pathogen. Although MERS, bird flu, and Ebola virus disease are currently not easily transmissible among humans, a few mutations may change this. Moreover, there may be many pandemic threats out there that we do not even know about yet.

Hence, a pandemic that spreads like COVID-19 is a realistic option. Notably, there are pathogens that are much more contagious than SARS-CoV-2. The basic reproduction number R of SARS-CoV-2 is estimated to be between two and five, which means that one infected individual infects on average another two to five people. For comparison, the R number for measles virus is estimated to be 12-18. Thus, a pandemic that is as deadly as Ebola virus disease and that spreads like the measles is the scenario we need to be prepared for.

COVID-19 has taught us that we do not have effective global surveillance systems that enable us to identify pandemic threats early enough. When the world started to act, it was too late to prevent the COVID-19 pandemic.

COVID-19 has also shown us that there is still no quick route towards effective antiviral drugs. More than a year into the pandemic, the prospects of drug treatment remain very limited.

Development of effective vaccines is the current big success story. However, it will take a long time, before a significant proportion of the world population is vaccinated. Hence, the vaccine success is limited to a small part of the global population. It is also not clear how long vaccine-mediated protection will last. Moreover, new variants that are not covered by previous vaccines may endanger the long-term success of vaccination programmes.

Even more concerning, we have simply been lucky that the current vaccines are actually effective. Nobody was able to predict with certainty whether the vaccines would work before the actual clinical trial results were revealed. Vaccines against other pathogens including HIV, Dengue virus, and hepatitis C virus have not been successful, although they induce a similar immune response. Thus, vaccines may not come to our help in the same way in the next pandemic.

Another lesson from COVID-19 is that the only time, at which we could have got rid of it, was right at the beginning. A strict worldwide lockdown for a few months immediately after the first COVID-19 cases had been detected would have most probably eradicated the disease and spared us the experience of the last 16 months and everything that is still to come.

Hence, the best protection from future pandemics, which will inevitably happen and may be much deadlier than COVID-19, is an improved surveillance system together with a functioning strategy that enables the world to go into a temporary lockdown that prevents new pathogens from gaining a foothold in the human population. This requires transparent and timely reporting procedures on suspicious disease outbreaks, viable plans for how to maintain essential supplies for a limited period of minimal human-to-human contact, and a strategy to protect the economy. If we establish such a system, we can stop future pandemics before they really start.