Covid, is it true that the contagion curve is slowing down? – Corriere.it

Is the growth of the contagion curve slowing down or not?
There have been small positive signs in recent days. But it is still too early to understand if it is a real trend or not. The most important data to observe the so-called Rpt, the percentage of positives over the number of swabs performed. A figure that is not affected by the continuous fluctuations in the number of controls. Since November 9, when it had reached 17.1%, this figure began to decline after practically continuous growth throughout the month of October. a sign that pushes me to have a modicum of optimism, says Enzo Marinari, a Physics professor at Sapienza in Rome, who along with some colleagues from his department has been monitoring Covid data in Italy for months.

Yesterday, however, there were new negative signs. So isn’t it true that the situation is improving?
Yes, yesterday the percentage of positives in the swabs made rose to 16.2% compared to 14.6% the day before. a figure that goes against the trend but is still not enough to speak of a true change of course. It could be a physiological oscillation within a downward trajectory. If in the next two or three days this ratio continues to increase, then we would be facing a true trend reversal. And that would not be a good sign.

But what must happen in the next few days to confirm that the situation is really improving?
In addition to the relationship between positives and the number of swabs, there are two other indicators to check. Trivial, if you will, but decisive: the number of deaths and the number of hospitalizations in intensive care. In the coming days they will continue to increase because there is a lag between infections and deaths. But in a few days they will have to start descending, explains Professor Marinari. Both for the health of hospitals and because they are the only indicator that does not need too many interpretations.

But when should this happen?
The precise moment is difficult to indicate. It can be said that for a week the number of deaths, that of those hospitalized in intensive care and also that of those hospitalized in so-called medical areas, must continue to increase. Then the descent should begin. Some believe that some signs should be seen sooner, in four or five days. And who on the other hand thinks that we will have to wait more, up to ten days.

Can this trend be considered the effect of the measures taken by the government in recent weeks?
It is reasonable to think that the cautiously positive trend of the contagion curve is the effect of the measures decided by the government on October 24, with gradual closures region by region. Even with the first wave, it was necessary to wait 15/20 days to see the effect of the containment measures adopted.

But could it be a negative sign?
the most worrying hypothesis but for the moment it cannot be ruled out. Giorgio Parisi, president of the Accademia dei Lincei, world famous physicist, colleague and friend of Professor Marinari, whom we heard earlier, illustrated it three days ago in Parliament. So far we have said that the growth of new positives would slow down as we approach the peak of the epidemic. In short, because the worst is over. But it could also be that the tracking system is increasingly unable to find infected people. It would mean that the virus is still working but we cannot intercept it, or even read it. A really disturbing scenario.

How to rule out this hypothesis?
The acid test is always the same. If in a week (although we have seen that it could be a few days less or a few more days) the number of deaths and ICU patients drops, it will be a positive sign. Otherwise, it means that the situation is out of control.