Università degli studi di Modena e Reggio Emilia

A study on scientific correlations between first and second wave of COVID-19 pandemic

A study carried out by Unimore researchers has explored the correlations between the first and the second wave of SARS-CoV-2 pandemic, and came to the conclusion that, where the number of cases every one hundred thousand inhabitants was higher than 500, the second wave highlighted a clearly reverse pattern, as it appeared to be the more mitigated, the stronger had been the intensity of the first wave. With the collaboration of also foreign researchers, the study has been published on the prestigious international scientific journal Environmental Research. One of the most likely explanations for this odd event is the fact that, during the first wave, an immunity not so far from the so called “herd immunity” was reached, or that it hit the so called “super-spreaders”, i.e. individuals who are mainly responsible for the epidemic transmission.  The study was signed by Professor Marco Vinceti and Dr Tommaso Filippini of Unimore, who have benefited from the collaboration of Professor Nicola Orsini of the University of Stockholm, Professor Kenneth Rothman of Boston University, and Silvia Di Federico, a graduating student in Medicine at Unimore.

Those areas of the Country that had suffered most the consequences of the spread of the first wave, have appeared to be definitely more sheltered during the second one. The observation comes from and is explained through a study by hygienists of the Department of Biomedical, Metabolic and Neural Science (DSBMN) of Unimore within an international collaboration, promoted by Unimore itself. The study was taken over and is now being published on the prestigious international journal Environmental Research.

Authors of the study are Professor Marco Vinceti and Dr Tommaso Filippini, hygienist and epidemiologist doctors of the Public Healthcare Department of DSBMN, who have downloaded the entire national database on the incidence of the SARS-CoV-2 infection broken down by province, which is freely available at the Italian Civil Protection.

The result was a database containing the incidence by provincial population in the periods of February-may and September-October 2020, thus taking into account also social-demographical factors such as the ageing index, the proportion of single-person households, and resident mobility.

It is undoubtedly the first rigorous analysis of the relations between the first and the second wave of COVID-19 in Italy, and of the epidemiological-statistical links between them. 

Unimore Professor Marco Vinceti explains that “During the last months, i.e. when the second and third waves of COVID-19 hit our Country, several commentators and communication media observed that areas that had been severely hit by the first dramatic pandemic wave in spring 2020, including the provinces of Lodi, Bergamo, and Piacenza, were relatively little affected by the subsequent upsurge of the SARS-CoV-2 infection. The reason for this outcome is still unclear and most of all, a systematic analysis of this phenomena, i.e. of the relations between the intensity f the first and second wave applied to the entire national territory, had not been carried out”.

Based on a statistical procedure that had been specifically developed for this study by Professor Nicola Orsini of the Karolinka Institute of Stockholm and by Dr Filippini of Unimore, it was possible to compare the two waves of Covid-19 in Italy. The results obtained, relating to the entire national territory broken down by province, allowed researchers to observe a direct correlation between the two waves up to an incidence in the first one of approximately 500 cases/100,000 residents. In addition to that incidence, the second wave highlighted a clearly reverse pattern, as it appeared to be the more mitigated, the stronger had been the intensity of the first wave.

According to the authors, the interpretation of these results left the ground open for three hypotheses: 1) during the first wave, an immunity was reached that was not far from the so-called ‘herd immunity’ (at least 50-70% of population, for this infection), even though the antibody seroprevalence levels of national investigation by ISTAT highlighted definitely lower humoral immunity rates, and in any case not higher than 5-10% even in most severely affected areas, probably due to a cell specific immunity or an immunity ‘crossed’ with other coronaviruses; 2) the first wave has selectively hit the so-called ‘super-spreaders’, i.e. the individuals that are mainly responsible for the transmission of the epidemic, therefore limiting their role during the second wave due to their previous post-infection immunisation; 3) in the most affected provinces, the population adopted stronger precautionary measures compared to the other geographical contexts.

“Based on the available elements, the authors believe that this last hypothesis is unlikely to be true.

In addition to Professor Nicola Orsini, an Italian biostatistician and professor in Stockholm, the study saw the collaboration of Professor Kenneth Rothman, a US epidemiologist at the Boston University, and Silvia Di Federico, a graduating student in Medicine and Surgery from Carpi. The study was carried out also thanks to the contribution of Fondazione Cassa di Risparmio of Modena, through the funding of the University Fund for the Interdisciplinary FAR-Research.

Professor Marco Vinceti commented on the work by stating that “the study was as fast in terms of design and realisation as it was important for us. Indeed, we wanted to try and ‘read’ the epidemic progress in real time by analysing the waves following the first one and, based on such epidemiological trends, immediately identify the factors that could predict and most of all prevent the occurring of new waves. I think that what we need to understand now is whether the reasons behind the inverse correlation between the two waves that we have found out are of an immunological or more strictly epidemiological nature. Our study also confirms the importance of the availability of so-called ‘open access’ data, including what we were able to retrieve and download from the websites of Civil Protection and ISTAT, for the accomplishment of environmental epidemiological studies that are directly relevant for public healthcare. Ultimately, I would like to thank this profitable international collaboration established during these months on COVID-19 epidemiology between Unimore, the Karolinska Institute and the Boston University, and enriched, on this occasion, by the contribution of one of our graduating students in Medicine”.

On his side, Dr Tommaso Filippini added that “Being able to carry out a more in-depth study on the progress and correlation of the first two waves of this pandemic is certainly an added value on a Public Healthcare perspective. Indeed, a deeper understanding of the epidemic dynamics, along with the study of other determinants like environmental and meteorological factors, and the characteristics of the population affected, will help us get a better awareness of what we could expect with regard to the progress of future epidemics on a global scale. This also with the purpose of organising the response of healthcare services in a faster and more efficient way to minimise the negative effects on population, especially for the most fragile categories such as the elders and people suffering from chronical diseases”.

Categorie: International - english