Looking back to the future? Possible pandemic scenarios from the past with relevance for autumn/winter 2021, and the years ahead
In many places the current coronavirus pandemic is the most severe pandemic since the 1918 influenza pandemic (“Spanish flu”). In many European countries before 2020, past experiences with pandemics had not been sufficiently studied and were no longer present in the minds of the general public or authorities. This article highlights scenarios from the past that may offer guidance as we move towards autumn and winter 2021. High quality morbidity data from the Swiss canton of Bern 1918-1930 is re-used here and complemented with similar data from 1957, SARS-CoV-2 data from 2020, as well as temperature series for all three years. A first possible scenario that emerges from experiences in all three pandemic years is that the onset of the fall waves at the beginning of October, occurred 0-2 weeks after the first drop in temperatures at the end of September (calendar week 39). This temporal coincidence can also be coincidental, and does not imply causality. However, this risk is also present for the coming autumn of 2021, all the more so if the case numbers will not be low everywhere then because of the delta variant. When temperatures start to fall, people will stay indoors more, which will increase the risk of infection for the unprotected or only partially protected subgroups of the population. In the winter of 1920, the influenza virus returned in the form of a relatively strong “echo” wave probably due to incomplete immunization of the population and/or virus mutations, and thereafter in the form of milder seasonal waves. This is a second scenario that many experts also consider possible for SARS-CoV-2. We do not know yet what will happen in autumn/winter 2021 and in the years to come. However, the past at least provides some scenarios of what happened in partly comparable situations in 1918 and thereafter. To not at least consider these possible scenarios in pandemic planning for the coming period would be a missed opportunity.