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“Our R0 for coronavirus is 0.75, below the national average of 0.80.” The news gives some satisfaction to Lombard Vice President Fabrizio Sala, who wants to emphasize in this way “the behavior of the Lombards who stopped with the confinement and then they resumed their activity, respecting the measures. Because we cannot die from Covid or starve. We have to react with the head and the Milanese are using the head ». Considerations that return to the starting point, that is, to that R0, the parameter to which we are all hanging. What has different implications, not so certain statistical bases and political projections to verify.
Parameters R0 and Rt
We did not have time to familiarize ourselves with the R0 index (erre with zero), which immediately specified by the Instituto Superior de Salud specifies: “It is more correct to speak of Rt”. The difference is said soon. R0 was measured at the beginning of the epidemic and is the average number of secondary cases generated by an infector. At first, in the northern regions, it reached 3. It means that one positive person infects three on average. How about RT? It is R0 over time, after the containment measures have taken effect. When the index falls below one, it means that the infection decreases. But are we sure they are reliable parameters? Epidemiologists themselves, like Alessandro Vespignani, take it with the springs: “Behind this blessed R0, he explained, there is such a complex forecast that we are a bit like meteorologists.” The first factor to consider is the number of swabs: the more they are made, the more the margin of error decreases.
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The asymptomatic
The second is that it does not include asymptomatic patients. Therefore, there is an estimate, inaccurate, but useful to have a general picture. But how does the rate decrease? “For two reasons – explains Stefano Merler, epidemiologist at the Kessler Foundation – due to the lack of contact between people and, therefore, thanks to confinement. And because it increases the number of immune, spontaneous healing. “It is difficult to bring it to zero, but it can keep it under control:« If it is at 0.5, you can also allow yourself to double the number of infections. Even though there is no magic formula » In phase 2, monitoring an increase in infected people, we will intervene at the local level: “We will verify in a few days a possible increase, which will nevertheless be contained. At that time it will be possible to intervene at the regional, provincial and aggregate level of the municipalities” .
The case of Lombardy and other regions.
According to Lombardy data, the region’s RT is 0.75. For the latest ISS data, from April 27, however, it is at 0.53. Why this difference? “The data is the same, explains Sala, the difference depends on the algorithms used. Our numbers are the result of the elaboration of our researchers and average the last three days. But the substance does not change. And is that the Lombards hold up well. There are four million citizens at work. However, only 60 percent are on the move, a sign that smart work is having a positive impact. ” Does the fact that a region is below the average authorize new openings? “They are political elections – says Merler -. But keep in mind that there are two factors that go in the opposite direction: the number of infected and the number of the immune. In Lombardy, the first is high, but the second is also high. Basilicata it has few infected, but if the infection develops, it would have a wider potential audience. Then you have to balance. “It is also true that the percentages must be calibrated on the absolute number of the population and on the distribution in the territory. For scientists and the government, the maximum threshold of Rt to allow citizens to move between regions is 0.2. Looking at the ISS data, we are not very close, but not even far. The only region below is Umbria, 0.19. Basilicata continues with 0.35 and Trento at 0.42. But the positive is that, including Molise in the lead at 0.84, they are all below the threshold. Enough to give some relief, not enough to go back. r to normal.
May 5, 2020 (change May 5, 2020 | 10:31 pm)
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