The likelihood of experiencing Covid-19-like pandemics could double in the coming decades. This is the conclusion of a study published in the journal ‘Pnas’ in which a global dataset of historical epidemics that occurred from 1600 to today is assembled and examined, using new statistical methods to estimate the annual probability of occurrence of extreme epidemics. The analysis suggests that there is “a high probability of observing Covid-like pandemics”, that the probability of experiencing it in one’s lifetime is currently around 38%, and that this probability may double in the coming decades. An upward trend due to the increase – linked to environmental change – in the onset of diseases from animal reservoirs.
Experts start from an observation: today estimates of the probability of occurrence of intense epidemics based on the long observed history of infectious diseases remain “late or missing altogether”. Hence the idea of carrying out an analysis that spans 4 centuries. The first author of the study is an Italian: Marco Marani, University of Padua and Duke Unversity. The expert signs it with colleagues from Duke University and Marquette University (Milwaukee, USA).
“Knowledge of the intensity of outbreaks, defined as the number of deaths divided by the global population and the duration of the outbreak, and the rate of outbreak of infectious disease is needed to test theories and models and to inform the assessment of public health risk by quantifying the likelihood of extreme pandemics such as Covid “, the researchers highlight. Their analysis shows that “the annual number of epidemics varies by 9 times and shows systematic trends”.
The annual probability of an event with the intensity of the Spanish flu (1918-1920) varies between 0.27 and 1.9% from 1600 to today, while its average time of recurrence today is 400 years ( confidence interval from 332 to 489 years). The slow decay of probability with the intensity of the outbreak implies that extreme outbreaks are relatively likely, a property previously undetected due to short observational recordings and stationary analysis methods. “Using recent estimates of the rate of increase in the occurrence of diseases from zoonotic reservoirs associated with environmental change – the authors conclude – we estimate that the annual probability of occurrence of extreme epidemics may increase up to three times in the coming decades”.