Background Information

Disclaimer: This interview-section is not part of the official statement but provides responses of the authors to commonly asked questions. The content of this section is not explicitly supported by the signatories.

[Viola Priesemann, Germany]: The virus does not stop at the European borders, and a destabilized spread in one country puts a successful mitigation strategy at risk in a different country. Therefore, all countries profit if they jointly lower case numbers and then keep them low.

[Giulia Giordano, Italy]: Unfortunately, the virus takes advantage of the free circulation of all citizens across the European Union: if the infection spread is out of control in one of our countries, all the others will be affected too and individual efforts to curb the epidemic will be jeopardised. To avoid a ping-pong effect of exportation and reimportation of cases among countries, and still enjoy our freedom of movement, we need a common European vision and a shared commitment to lower the number of cases, and keep it low.

[Thomas Czypionka, Austria]: At the moment, every country acts according to its own rules. This was probably a viable strategy in the beginning, when we did not know what actually worked. We could learn from trial and error. But the evidence base has changed. Today, we know much more about the virus and about what works and what doesn’t. It is time for European leaders to develop common and coordinated goals and strategies, so that borders can be reopened without the risk of re-importing the virus.

[Michelle Kelly-Irving, France]: Europe is characterised by land borders and often freedom of movement between countries. These characteristics connect us to each other, but during a pandemic they pose a risk to the population because they facilitate virus transmission which can enter & leave countries and reignite a local epidemic. Together, with common objectives, we can work to get the situation under control in a way that is most adapted to each context. By working in a concerted way across European countries to keep case numbers low, sharing information, resources and knowledge, we will be stronger and better able to manage the COVID-19 crisis.

[Pirta Hotulainen, Finland]: We have done a lot of advocacy work in Finland aiming at SARS-CoV-2 suppression. One of the arguments against suppression in Finland has been that we cannot close the borders and then the virus will come back. Finland is the last corner in Europe, so we have somehow managed to control borders but it is clear that it makes travelling very unpleasant. Thus, we would be more than happy to see that the whole of Europe gets healthy again and we can start getting back to a more normal life.

[Mirjam Kretzschmar, The Netherlands]: It leads to more trust and support in the population if countries in Europe work together to reach a common goal, based on a common evidence based strategy. It is important to communicate goals and strategy very clearly.

[Eva Schernhammer, Austria]: If we have one thing in common with the pandemic it is that borders do not stop us - as Europeans we enjoy our commonality without borders. But to confront the virus, we must also act as if there were no borders, and a common European vision is needed.

[Ewa Szczurek, Poland]: Europe has so far shown little collaborative effort to contain the COVID-19 pandemic. A prominent exception from that rule is the joint strategy to purchase and disseminate the vaccines. We hope that this positive example can show that coordinated actions are possible.

[Ewa Szczurek, Poland]: The call asks the European governments to make three major shifts in their way of managing the pandemic:

  1. put the numbers not simply down, but really down. Here the number 10 per million is really crucial to practically realize what it means. In Poland, this means that as soon as we get 370 daily cases the alarm bells should go off. We are far away from these critical numbers now, all across Europe. It seems like the only way to achieve this now and fast is a strict lockdown across Europe. This should be a one time event, and our "final lockdown".
  2. do this in a coordinated manner. Again, what does it mean in practice? Putting low numbers in Germany only is not enough. Germany should make sure, the numbers are low in Poland. And Poland should make sure they are low in Germany.
  3. make sure to keep these really low numbers using modern containment measures. We don't want anymore lockdowns after the "final lockdown". Lockdowns prolonged in time cost a lot of money and health. We want money to be invested in prolonged efficient, widespread maintenance of low numbers, and efficient implementation of the vaccine (see the illustration at the bottom of the website).

[Viola Priesemann, Germany]: COVID-19 does not stop at the borders. And an uncontrolled spread in one country puts a successful mitigation in other countries at risk. Hence, we contacted my European colleagues for support, and the response was truly overwhelming. Within days we had hundreds of signatories, and we could have gathered many more. We are looking forward to your feedback, and to your support! Please spread the word!

[Deepti Gurdasani, UK]: Low case numbers not only protect our health, and save lives, but also allow our society and economies to return to normal, as many examples across the world have shown us.

[Pirta Hotulainen, Finland]: To be honest, I would aim for a lower number. But maybe this is a more achievable number for most of the countries. The less cases, the better, this is the rule. With low cases, it is possible to control virus spread with mild actions, such as testing and tracing.

[Viola Priesemann]: This number marks a goal, not a strict upper limit. But why precisely a goal of ten?

  • First, low case numbers have all the advantages that we listed in our position paper.
  • Second, new case numbers must not overwhelm the testing and the contact tracing capacity of a country [1]. In many countries, the testing can handle about 10 daily new infections per million, but not 50 or more. The test-positive rate becomes too high. And the contact tracing is not sufficiently fast anymore.
  • Third, if surpassing the level of 10, then one still has some time before reaching the strict limit of about 50 daily new cases. This safety-margin of about two doubling times enables policy makers to prepare the necessary actions without haste should the numbers grow.
  • Fourth, at low case numbers, random fluctuations may lead to local eradication, thus to zero cases. Hence, locally and temporally, a region can profit from zero covid [1,2].
  • Fifth, if all neighboring regions reduce their case numbers by a factor 2, then your own region will automatically reduce its case numbers by a factor 2 as well - if behavior is not changed. This sounds like magic? No, it is the synergistic effects of low case numbers across Europe, and can be explained by simple math.
The math behind the stable level of case numbers: [3,4] First, for stability the effective reproduction number R must be smaller than unity (R<1). Thus: one person on average must not infect more than one other person. Given R<1, what does then determine the stability level of new cases N per day per million persons? In the simplest model, it is determined by two factors, R and the influx F of new infections from outside:
N = F/(1-R) This formula clearly states: If case numbers are low in your neighboring regions, then the influx F of new cases from that region is low, and your own region will profit: it will have low case numbers as well. Hence, under open borders, everyone jointly profits from low case numbers; in contrast, high case numbers in one region can endanger the stability in their neighboring regions.

[Matjaž Perc, Slovenia]: Although vaccines have been developed, it is unlikely that sufficient coverage will be achieved in due time to ensure population immunity before the second wave fully tapers off or even before a potential third wave starts in Europe. Although there are still several unknowns around vaccine efficiency and uptake, current data suggests that a vaccination coverage of 60-80% would be needed for herd immunity against COVID-19. Taking current resources into account, not just in terms of vaccine availability, but also in terms of the availability of human resources needed to run such a large-scale vaccination program, it is virtually impossible that a sufficiently high vaccination coverage will be achieved for Europe to be able to abandon other measures for mitigating COVID-19 infections.

[Thomas Czypionka, Austria]: In order to slow down population spread, a certain number of people need to be immune to the virus, called population immunity or herd immunity. However, there are several reasons why the existence of a vaccine will not contribute to reaching this population immunity soon and make other measures expendable in the coming months:

  1. The availability of vaccine doses is limited. Therefore, the majority of the population in each European country will not be vaccinated before summer.
  2. The sequence of vaccination in most European countries targets people at high risk first, e.g. residents in long term care facilities. But these people, due to limited mobility and social contacts, do not contribute much to population spread, so the virus will continue to circulate in the general population unhindered.
  3. In order to reach herd immunity, the vaccine not only needs to protect the person from contracting the disease, but block transmission as well. Current available evidence suggests that the first vaccines will not be able to block transmission completely, and may be able to reduce transmissibility. In other words, people that received their vaccination will be protected with high efficacy, but will be able to infect others to some extent. Transmission chains are not broken effectively, and people not vaccinated and people who do not develop a sufficient immune response to the vaccine will still be at risk.
  4. Last but not least, it is unclear how long immunity lasts, being after infection or after vaccination.

[Pirta Hotulainen, Finland]: Especially now when vaccines are here, every unnecessary death and LongCovid-case is too much.

[Sarah Cuschieri, Malta]: Unfortunately there is a lot of healthcare professional vaccine hesitancy apart for hesitancy within the community/population. Considering that healthcare professionals are reflected as "role models" to their patients, this might impact the uptake of vaccines. However, having said that, recently we conducted surveys to assess the seasonal influenza uptake last year (2019), this year (2020) and the intention to take Covid-19 vaccine among healthcare professionals [5]. It was observed that although hesitancy is still present, a higher healthcare professional’s proportion expressed an intention to take both the influenza and COVID-19 vaccine this year. So it is expected that the same attitude will be present within the community. However, the COVID-19 vaccine being a "new" vaccine will still carry concerns among both the healthcare professionals and the general public, which further supports our current statement.

[Deepti Gurdasani, UK]: The impact of vaccines on transmission will depend on many factors, including vaccine uptake, vaccine efficacy (in preventing transmission), and the duration of immunity provided by vaccination. It’s worth remembering that no infectious disease to date has been eradicated by vaccination in a short period of time - indeed, most have not been eradicated at all, even after decades since vaccines were developed. Vaccines are part of a broader public health strategy, not the end all, and it is likely that transmission will continue for a long period of time. It’s also worth noting that vaccines have not been licensed for use in children yet, who form a significant proportion of the population, and play an important role in transmission. It is important we use multi-pronged strategies to control the virus, rather than counting on vaccines alone.

[Matjaž Perc, Slovenia]: Job one at this point is to get the current numbers of active cases down across Europe. Then we have to remain vigilant, so that whenever new cases start to emerge, we are prepared to act fast and resolutely. This will prevent a third wave, as well as keep hard lockdowns geographically and time-wise limited.

[Eva Schernhammer, Austria]: The more people will have developed immunity i.e. received the vaccine, the less strict will measures eventually have to be to keep the numbers at the balancing level of not overwhelming health care. A problem with this approach in Austria is, however, that currently, our ICUs are filled by relatively young persons (average age at AKH ICU around 60 years), so by starting to vaccinate older people first, it will not change the ICU dynamics for a while. Essentially, the close to overwhelming our ICUs will likely occur (again) before sufficient individuals have been vaccinated. This speaks for implementing another hard lockdown as soon as possible.

[Thomas Czypionka, Austria]: In our modelling, the most effective way seems to be a lockdown followed by effective contact tracing (apart from physical distancing, masking and moderate contact reduction). In order for the subsequent contact tracing to be effective and efficient, post-lockdown case numbers need to be low. With such a strategy, a third wave can be avoided at minimal economic and societal costs.

[Pirta Hotulainen, Finland]: Europe needs a longitudinal and clear plan of what to do at each level. As soon as cases are pushed close to zero, we need to be careful, use masks and perform testing and tracing at an ambitious level. Screening of population to follow - if the case number will start increasing again - is a very good idea. Fast actions are needed.

[Deepti Gurdasani, UK]: There are many successful models to learn from from across the globe. There needs to be a long-term strategy, including effective find, test, trace, isolate and support systems. These systems can detect clusters of transmission rapidly and prevent forward community transmission. As we outline in our letter, these systems will require cases to be brought down to low levels first. The success of such systems is dependent on rapid testing, effective rapid backward and forward contact tracing, as well as adequate financial and practical support with isolation to ensure high compliance with this. We also need to focus on better quarantine at borders, widespread mask use, and mitigatory measures to reduce transmission in schools. Good consistent public communication is a key part of any such strategy.

[Viola Priesemann, Germany]: As soon as case numbers are low, it is important to keep them low. Otherwise the gain is soon lost. In practice, this means that local measures need to be taken as soon as a district or Landkreis crosses a threshold of 35 or 50. A potential blueprint is the five-level plan of Ireland [6]. If one does not counteract the local outbreaks, the spread gets out of control, and puts the successful mitigation in neighboring regions at risk.

[Eva Schernhammer, Austria]: As long as contact tracing (and isolation) can successfully be maintained, and thus COVID-19 contained, mitigation measures such as a lockdown can be avoided. Thus, and for other reasons as outlined in the Correspondence, it is crucial to be able and maintain the ability to contact trace

[Giulia Giordano, Italy]: The benefit of contact tracing is fundamental: once an infected has been detected, it is crucial to isolate and test all the people with whom the infected person has come into contact, so as to break as soon as possible the contagion chain. Of course, it comes at a cost: a dedicated infrastructure, including people and resources, is needed to trace contacts, while tracing apps may raise privacy issues. Also, testing and tracing works well only when the case numbers are low enough: the infrastructure cannot cope with huge case numbers. However, by testing and tracing, outbreaks can be early detected and suppressed, allowing us to live a more normal life in spite of the pandemic.

[Mirjam Kretzschmar, The Netherlands]: Contact tracing is essential because it is a targeted way of finding infected persons before they develop symptoms, and so can prevent a large part of their possible transmission to others. Contact tracing for SARS-CoV-2 only works, if it is fast enough because otherwise too many onward transmissions have already been generated by infected contacts of an index case before they are traced and isolated. Tracing has to catch up with the transmission process in order to be effective. This necessary speed can only be achieved, when case numbers are low, such that the tracing infrastructure is not overloaded. The speed can possibly be increased by digital methods such as apps, which reduce the time between test result of a case and successful isolation of an infected contact person. Also fast test results help making tracing and isolation faster.

[Thomas Czypionka, Austria]: There are two reasons why low case numbers are important for an efficient and effective contact tracing.

  1. Contact tracing requires a lot of personnel: WHO has issued a spreadsheet to calculate personnel needed [7]. For example, 1.500 cases per day will take more or less 10.000 contact tracers to handle. Staying on top of this much personnel gets more complicated with higher numbers and thus more ineffective.
  2. The close contacts of an index case need to be quarantined. Naturally, the more daily cases, the more people end up in quarantine for e.g. ten days, some repeatedly. Now, some of these people can still do their jobs from home. However, this is not possible in many industries, e.g. goods production, construction, trade, healthcare, personal services etc. In such cases, the contribution to production is lost, having a negative impact on GDP. As an example, take 2.000 independent cases per day each with five close contacts on average. Then each single day, 12.000 people need to self-isolate for ten days. If 50% of these people have work and 60% of those cannot work from home, nearly 30.000 person days are lost. What is more, many of the industries requiring manual labour provide lower-paid jobs, and lay-offs due to not being able to show up for work is a real threat in such cases. Inequality is thus increased.
Therefore, while it may be possible to stabilize infections at higher case numbers, this is not advisable, as tracing contacts gets more complicated and economic costs as well social consequences are substantial.

[Peter Klimek, Austria]: European countries can learn some lessons from Asian countries concerning how the efficiency of contact tracing can be increased, which in turn means that less stringent social distancing measures are required for achieving the same level of pandemic control. Contact tracing needs to adapt to a disease that primarily spreads in clusters, as it is the case with SARS-CoV-2. If 20% of infected cases are responsible for 80% of the infections, this means that the chances that a randomly picked infected person causes a superspreading event is only 20% whereas there is a chance of 80% that the infection has been acquired in such an event. Contacts therefore need to be traced “backwards” in the contact network to swiftly identify potential superspreading events. This can be done by asking targeted questions whether an infected person recently attended a family celebration, a fitness studio, a bar or other high risk settings for superspreading events. The use of all data sources that may facilitate this process should be considered (e.g. mobility or payment data).

[Michelle Kelly-Irving, France]: Contact tracing systems are vital to breaking chains of transmission, but they are resource-heavy. They require a large staff and a complex infrastructure. As well as tracing contacts in-person or using technology, key components of the system involve isolating cases and contacts in a supportive way. People need to be properly supported in order to apply isolation rules: support for their caring responsibilities, doing the groceries, receiving their medical treatments and workers need to receive paid-sick leave. Such a system of contact tracing, isolation and support can therefore only work efficiently if case numbers are kept at their lowest through prevention measures.

[Viola Priesemann, Germany]: Contact tracing can contribute considerably to stopping infection chains, and to lowering the dark figure [3]. However, it has to be fast [8], hence it works best at low case numbers. With efficient contact tracing in place, we can have more contacts in general. However, it seems that contact tracing is not sufficient to have contacts as before. A moderate reduction of contacts needs to be maintained.

[Giulia Giordano, Italy]: One could argue that a golden target would be, for instance, 5000 tests per million people per day. Actually, it would be reasonable to dynamically adjust the number of daily tests depending on the ratio between positive tests and total number of tests: if this ratio is too high, let's say above 5% [9], this is an indication that we should be testing much more. Sufficient testing is key to prevent the pandemic from going out of control.

[Viola Priesemann, Germany]: Even if case numbers are low, testing has to be continued to be able to detect a novel outbreak sufficiently early. Therefore, we propose to conduct at the very least 300 tests per million people per day.

[Mirjam Kretzschmar, The Netherlands]: Not only the number of tests is important, but also who is tested [10]. Targeted testing can be much more efficient, if it is done in a smart way and at the right moment. For example, we should design ring testing strategies, where all people in a ring around a diagnosed case are tested rapidly, such that undetected infections can be found. Testing at certain locations or of risk populations, or testing of bridging individuals in a network (those who connect different subpopulations) may also be effective strategies.

[Matjaž Perc, Slovenia]: Throughout history, we have attempted to stop epidemics by means of community lockdowns. Be it the shutting down of infected family houses during the mid 14th century plague pandemic, or the lockdown of different residential areas across major Chinese cities during the first wave of the COVID-19 pandemic. But research shows that community lockdowns are effective only if the links outside of the communities are truly completely sealed off. The benefits are inferable only beyond 90% lockdown effectiveness. And even then the peak of the infected curve decreases by only 20% and its onset is delayed only by a factor of 1.5. The complex connectedness of modern human societies, which enables the ease of global communication and the lightning speeds at which news and information spread, also makes it very difficult to halt epidemic spreading with top-down measures, such as community lockdowns. What actually works, and what we should be aspiring to, is bottom-up endogenous self-isolation and social distancing. Unfortunately, the latter can not be as easily imposed or controlled as top-down measures, but they are absolutely crucial for an efficient suppression of cases. In the absence of this everything else, such as shutting down public transport, schools, restaurants, and factories, is ultimately bound to fail. But this is not to say that we do not need top-down measures -- we do need them, but under the understanding that they enable us to enact what actually works, which is self-isolation and social distancing.

[Giulia Giordano, Italy]: I believe the best strategy is a wise combination of physical distancing (such as targeted lockdowns), which is indispensable to drastically lower case numbers, and of widespread testing and contact tracing, which is fundamental to keep case numbers low [11]. Of course, individual responsibility, hygiene, use of masks and reduction of non-indispensable contacts are fundamental all the time.

[Peter Klimek, Austria]: If case numbers are so high that the test-trace-isolate (TTI) capacities become overwhelmed, the adoption of widespread social distancing measures affecting all areas where people gather in smaller or larger groups indoors over longer periods of time (“CCC settings”: close, closed, crowded contacts) become inevitable. European countries that implemented such hard lockdowns to combat the second wave this autumn were able to more than halve their case numbers after three weeks; Ireland was able to bring its numbers down to a third of the peak levels, France brought it down to a fifth. A potential strategy could be to implement hard lockdowns to a point where TTI becomes operational again and the remaining high-incidence regions can be controlled with (combinations of) specific and more targeted interventions (ranging from partial lockdowns over frequent mass testing to cordon sanitaires).

[Mirjam Kretzschmar, The Netherlands]: It is essential that the awareness in the population of the importance of the basic hygiene measures (mask wearing, hand hygiene, keep distance) is kept up. Even if these measures alone cannot keep case number low or stop an outbreak, they contribute substantially to lowering the reproduction number [12].

[Viola Priesemann, Germany]: We see clearly that a strong lockdown is efficient. We know it both from the first and second waves, as well as from modeling [13]. A weak lockdown, however, has to be in place increasingly longer, or is not effective at all. Hence, synchronizing as many measures as possible is really helpful to get over with the lockdown soon. Which measures do we have? Well: After 10 months of pandemic in Europe, we know sufficiently well what to do.

[Eva Schernhammer, Austria]: Eliminating an infectious disease i.e. global eradication has hardly ever happened in our history (smallpox); but controlling the pandemic is likely possible, even if seasonality and the need for updated vaccines each year emerge for COVID-19. With adequate political as well as societal support, a suitable vaccine, as well as other factors, eradication of COVID-19 is theoretically also possible.

[Sarah Cuschieri, Malta]: The population support is adamant since it is already reported that unless 75-80% of the population get vaccinated, population immunity will not be reached. However, if this is achieved, COVID-19 may become endemic.

[Deepti Gurdasani, UK]: There are several countries across the globe that have managed to reduce case numbers to zero or near zero, and countries such as New Zealand and Taiwan have achieved elimination for relatively long durations of time. This has resulted in much lower impact to public health, life returning to normal, and rebounding of the economy. These models show us what can be achieved with a clear long term vision, good communication, and an evidence-based approach.

[Mirjam Kretzschmar, The Netherlands]: In my opinion, it will be very hard, if not impossible to reach elimination or even eradication. It will depend much on how long lasting immunity after infection or vaccination is. There are a number of factors that make elimination very difficult: transmission from presymptomatic and asymptomatic persons, short doubling times of uncontrolled epidemics, and possibly waning immunity. For smallpox, the only disease that has been eradicated, these factors were more favorable: full lasting immunity after infection or vaccination, relatively long generation interval (time between infection of a case and infection of his source), and only a short prodromic phase.

[Viola Priesemann, Germany]: If we reach local elimination, then we can profit from the “Zero-COVID” advantages. Getting case numbers below the 10 per day per million people is an important first step. And in fact, throughout summer, a number of regions in Germany and Europe had zero COVID-19 cases over weeks. However, the zero could not be maintained. Hopefully, we will reach and maintain it latest in spring 2021.

[Matjaž Perc, Slovenia]: If the currently ongoing second COVID-19 wave across Europe has taught us anything it is that it definitely does not pay off to wait with lockdowns because the economy will suffer. This was the argument in many EU countries, i.e., let us wait a bit with the measures until the summer season is ongoing. But the price we are all paying now, and certainly not just in economic terms, is much higher than whatever we have saved in those 2-3 weeks when a lockdown was long due but postponed due to economic reasons.

[Pirta Hotulainen, Finland]: With this virus, we do not have any good options. In my opinion the best option is to push cases down fast and then keep them there with effective testing and tracing. This is, however, difficult. Still, lockdown is less harmless and more effective (needs shorter time) when done in time and not at the last minute when the hospitals are already full.

[Andreas Peichl, Germany]: The economic costs of the pandemic are increasing in the duration of lockdown measures and they do so more than proportionally [14]. Moreover, uncertainty and frequent policy changes are bad for consumer and investor confidence and are harmful for the economy. Hence, it is in the common interest of health and the economy to shorten the necessity and duration of lockdowns by bringing down infection numbers and keeping them low through testing and contact tracing.

[Eva Schernhammer, Austria]: Tomas Pueyo's suggestion of the hammer and the dance only works if people dance the right dance. Currently, a hammer, followed by another hammer if/once needed, seem to be the better working way to tackle the pandemic.

[Giulia Giordano, Italy]: We have two choices. First: we act immediately and then we release the lockdown once case numbers are low enough. Second: we postpone, until the lockdown becomes inevitable due to saturation of hospitals and intensive care units, and unbearable numbers of daily deaths. In both cases, the economic burden is comparable - and may be even worse in the second case, because the lockdown needs to last much longer if it starts when the number of cases is huge. But a prompt intervention drastically reduces healthcare costs and saves many lives.

[Thomas Czypionka, Austria]: We now know more about the virus and its transmission and can act accordingly to keep at least parts of the economy running without increased risk of infection. International trade is also less affected. Many businesses as well as societies as a whole have adapted. Therefore, costs of a lockdown are much lower today than in the first wave. Low case numbers in turn create low quarantine numbers over an extended period of time, and this is what makes the real difference economically. In other words, a lockdown that brings cases down effectively pays off in the long run.

[Peter Klimek, Austria]: The unfortunate situation that we observe in the second wave in Europe is that the only sustainable way to substantially reduce case numbers in the second wave have been hard lockdowns. The task is therefore to ensure that we minimize how long and how broad we require hard lockdowns in order to minimize their economic burden. A broad body of research suggests that this is best achieved by reacting early to localized outbreaks with stringent regional measures as a means to prevent the need to lock down entire countries, which is only possible with low case numbers.