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Study points to factors that helped the initial dissemination of Covid-19

Publicado em 24 junho 2020

When it left the Chinese province of Hubei for Europe and its Asian neighbors – between December 2019 and January 2020 – the coronavirus SARS-CoV-2 found in some regions of the globe particularly favorable conditions for its spread.

After analyzing data from 126 countries, including Brazil, researchers from Unicamp (Universities of Campinas) and Barcelona identified a set of factors that would have favored the rapid spread of the virus in the initial phase of the epidemic, that is, before policies were adopted to contain contagion.

According to the study, supported by Fapesp, among the factors that contributed to the higher initial growth rate of covid-19 are the low temperature and, consequently, the population less exposed to the ultraviolet rays of the sun and with a lower level of vitamin D in the blood.

Other points identified by the research were: higher proportion of elderly people and, therefore, higher life expectancy; greater number of international tourists in the early days of the epidemic; and early onset of the outbreak (countries where the disease first arrived took longer to take preventive measures).

Other indicators are the higher prevalence of lung cancer, cancer in general and COPD (chronic obstructive pulmonary disease); higher proportion of obese men; higher rate of urbanization, higher consumption of alcohol and tobacco; in addition to greeting habits that involve physical contact, such as kissing, hugging or shaking hands.

In an interview with Agência Fapesc, Professor Giorgio Torrieri, from the Gleb Wataghin Physics Institute (IFGW-Unicamp) and co-author of the article published on the medRxiv platform, still without peer review, spoke about these indicators.

“We chose as the starting point of our analysis the day on which each country registered the 30th case of Covid-19 and analyzed the following days [entre 12 e 20 dias, dependendo do país]. The objective was to understand what happened at the stage when the disease grew freely, almost exponentially ”, he explains.

According to the researcher, the proposal was to apply statistical analyzes commonly used in the field of physics – among them simple linear regression and the calculation of the determination coefficient – to try to understand what happened at the beginning of the pandemic. The data used in the analyzes came from a variety of sources – much of it from a public repository known as Our World in Data.

“The idea was to evaluate the following: if nothing was done to contain the disease, how fast would the virus spread in different countries or in different social groups? Do factors such as temperature, demographic density, urbanization and health conditions of the population influence the speed of contagion? ”, He argues.

Trusted sources

Some studies suggest that the BCG vaccine against tuberculosis may have some protective effect in the case of Covid-19. The analyzes made by researchers from Unicamp and the University of Barcelona indicate the existence of a weak correlation between the two variables (rate of immunization against tuberculosis and rate of contagion by SARS-CoV-2).

According to Torrieri, however, it is possible that the result was harmed by the lack of reliable data in countries where vaccination is not mandatory.

“When we exclude countries without vaccination data, the correlation is weak. But when we include these sites in the analysis and assume that they have a low rate of immunization, the correlation becomes stronger ”, says the researcher.

For some of the factors analyzed – among them the prevalence of diseases such as anemia, hepatitis B (in women) and hypertension – the researchers identified a negative correlation. That is, in countries with a higher proportion of hypertensive patients, for example, the initial contagion rate for SARS-CoV-2 was lower.

“We can imagine that in these places there is more cardiovascular disease and, therefore, less life expectancy”, evaluates Torrieri.

Factors without influence

Among the factors analyzed that did not correlate with contagion (neither positive nor negative) are: number of inhabitants; prevalence of asthma; population density; vaccination coverage for polio, diphtheria, tetanus, whooping cough and hepatitis B; prevalence of diabetes; level of air pollution; number of holidays; and proportion of rainy days.

In the case of the Gross Domestic Product (GDP) per capita, as explained by Torrieri, the correlation was positive only in amounts above 5,000 euros.

“GDP is related to the quality of public infrastructure. The higher a country’s GDP per capita, the better the health and housing infrastructure, for example. But below 5,000 euros, it probably made no difference because the infrastructure is of low quality ”, evaluates the researcher.

Variables analyzed are correlated with each other

As the authors point out in the text, several variables analyzed are correlated with each other and, therefore, they are likely to have a common interpretation and it is not easy to separate them.

“The correlation structure is quite rich and not trivial, and we encourage interested readers to study the tables [do artigo] in detail, ”they say.

According to the researchers, some of the correlations pointed out are “obvious”, for example, between temperature, UV radiation and vitamin D level. “Others are accidental, historical and sociological. For example, habits such as alcohol consumption and smoking are correlated with climatic variables.

Similarly, the correlation between smoking and lung cancer is very high and probably contributes to the correlation of the latter [o câncer] with the weather. Historical reasons also explain the correlation between climate and GDP per capita ”, say the researchers.

Government influence

Although it is impossible for countries to change some of the variables studied, such as climate, life expectancy and the proportion of elderly people, for example, their influence on the spread of the disease must be taken into account in the formulation of public policies, helping to define strategies testing and social isolation, they argue.

Other variables, according to the authors, can be controlled by governments: testing and isolation of international travelers; restriction of flights to regions most affected by the pandemic; promoting habits of social detachment and campaigns to reduce physical contact while the virus is spreading; and campaigns aimed at stimulating vitamin D supplementation in the population, reducing smoking and obesity.

“We also emphasize that some variables pointed out are useful to inspire and support research in the medical field, such as the correlation of contagion with lung cancer, obesity, low vitamin D levels and different blood types and type 1 diabetes. This definitely deserves further study. in-depth, with patient data ”, conclude the scientists.

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