Covid-19: Surveillance systems for the new normal

What have we learnt about surveillance after two years of a pandemic? Will we have the numbers and information to identify, early enough, new surges of the pandemic? Nothing is less sure,1 but let’s hope that strong surveillance systems will be part of our “new normal.” In many European countries, measures to limit the spread of SARS-CoV-2 infections are being progressively lifted. If we are lucky enough, and thanks to vaccination and a partial herd immunity,2 the covid-19 related burden could be manageable in the coming months, and eventually decrease. But the uncertainty remains very high, owing to new variants or falling immunity, for example, and we have to track the signs of new waves. We should try to do much better than before. We need an efficient and reactive monitoring system, which could be made of three layers. The first and basic layer is a declaration and sentinel system to track new cases by healthcare providers, enabling control of local outbreaks and identification of new variants. Because cases diagnosed by healthcare providers are exposed to surveillance bias,3 the second layer should be repeated population based surveys, based on random sampling and using antigenic or PCR tests, to assess the proportion of people infected across time. This is the only way to have a reliable estimate of the dynamics of virus spread4: modelling is not enough. Third, population based seroprevalence studies would be useful to assess the evolution of population level immunity.5 To make this system work, we would need to strengthen the culture of surveillance and improve evidence communication.6 The coming months will be critical to see if the virus looks roughly like influenza, which seems to be the hope of many health authorities. Without a strong information system, however, this hope will be neither challenged nor confirmed. Numbers matter1 because without them we will not be prepared for the next waves.