Projections made with a mathematical model developed at the State University of Campinas (Unicamp) indicate that the adoption of lockdown mandatory in the State of São Paulo to contain the coronavirus it will be inevitable if the level of social isolation does not rise significantly in the coming weeks, starting as early as Tuesday (12/05).
Between May 8 and 10, on average, 1,839 new daily cases of Covid-19 were recorded across the state, with 1 033 in the capital alone. There were also 93 deaths in the capital and 168 in the state (also on the average of the three days).
If the contagion rate (R0) – which is the number of people to whom an infected person transmits the virus, on average – observed in the 30 days prior to May 10, at the end of June São Paulo will account for 53.5 thousand new infections per day, being 20.8 thousand daily cases only in the city of São Paulo. The number of daily deaths will reach 2,500 in the state, of which 1,100 will occur in the city of São Paulo.
During this period, it is estimated that the number of new cases doubled every 11.5 days for the state and every 12.9 days for the capital. For deaths, the number was doubling every 13.5 days in the state and every 14.7 days in the city.
.The calculation was made considering the real data of growth in the number of cases over the last month, which indicate a contagion rate of 1.49 for the state and 1.44 for the city of São Paulo. That is, at the end of April, every 100 infected paulistas transmitted the new coronavirus to almost 150 people, on average (over a period of about 7.5 days after being infected, according to the model used).
“These projections have a great chance of being underestimated, because the level of isolation has been falling since the beginning of April and, between the 5th and the 9th of May, it did not exceed 50%, which will cause the rate of contagion to increase. This will be reflected in 15 or 20 days in the number of new cases, then on the number of deaths ”, says mathematician Renato Pedrosa, professor at Unicamp’s Geosciences Institute and coordinator of the Special Science, Technology and Innovation Indicators Program at Fapesp . “But even if the contagion level estimated is maintained until May 10, the projected values indicate that this month the public health system in the Metropolitan Region of São Paulo will reach the limit, since the level of ICU bed occupancy has already is above 80%. If the isolation is not expanded urgently, the state will have to adopt more drastic measures of containment, as occurred in Italy, or the situation will become untenable ”, he adds.
The estimates were made with a model developed by Pedrosa and described in an article available on the platform medRxiv in version preprint (not yet reviewed by scientists). The calculation allows estimating the transmission dynamics of Covid-19 in different locations, taking into account climatic variables (temperature and absolute humidity), population density and the timeline of the onset of the disease (date when the country or region reached the mark of 100 cases).
To develop the model, Pedrosa used data from 50 US states and 110 other countries, including Brazil. Countries were selected for which sufficient information was available to calculate the exponential growth rate in the period when the hundredth case of the disease was recorded. The meteorological information was obtained from a database of the National Oceanic and Atmospheric Administration (NOAA), an institution that is part of the United States Department of Commerce.
Data for the expansion of Covid-19 until April 10 came from two sources: the Center for Systems Science and Engineering at Johns Hopkins University (United States) and the European Center for Disease Control and Prevention, based in Sweden.
“Initial studies suggested that the new coronavirus would find it more difficult to spread in hot and humid countries. However, according to this model, the effect of climatic variables on the initial rate of expansion of the disease was not significant when the variables of population density and / or the date of onset of the disease were included [100º caso]. This confirmed the experience of Brazil and other countries that were in the summer period, with hot and humid weather, and suffered a severe expansion of Covid-19 ”, says Pedrosa.
“The date of the 100th case came up in an interesting way. The later this event occurred in a given location, the lower the initial rate of coronavirus expansion. A possible explanation for this finding is that, in places where the virus was slow to arrive, the population began to become aware of the need to adopt protective measures, such as washing hands, using gel alcohol, avoiding handshakes and agglomerations. And this slowed down the transmission speed even in the early stages, ”he says.
According to Pedrosa, once this effect is discounted, the population density of the different regions analyzed – measured by the number of inhabitants per square kilometer – became the most relevant variable to estimate Covid-19’s free expansion rate (that is, the speed with which it would spread if there were no mitigation measures). The more densely populated the region, the higher the rate of free contagion.
Attenuated coronavirus contagion
Based on these results, Pedrosa decided to estimate the rate of contagion mitigation that would be necessary to control the disease in all Brazilian capitals and the Federal District, depending on the population density of each city.
At the top of the list of the most densely populated in the country are Fortaleza (7 786 inhab./km2), São Paulo (7 398 inhab./km2), Belo Horizonte (7 167 inhab./km2), Recife (7 040 inhab. / km2) and Rio de Janeiro (5 267 inhab./km2). If no measure of social distance had been adopted to contain the advance of the new coronavirus in these municipalities, calculates the researcher, everyone would have a contagion rate greater than 5.8 and the number of infections would double in less than two days.
“To control the disease in the four most densely populated cities in the country, it is necessary to reduce the rate of free contagion by 84%, which would be possible with at least 60% of social isolation combined with the mandatory use of good quality masks, for example ”, Estimates Pedrosa.
According to him, the effect of the recent measures will take some time to be evaluated, which will delay the measures to be adopted, which are urgent and will have an impact, likewise, only in two or three weeks.
This content was produced by Agência Fapesp.