Hot Autumn

 

Not too many years ago,  "hot autumn" had a precise meaning in Italy. It was a way of indicating trade union uprisings/demands.

In our day, we are no longer preparing to see workers' revolts. Still, the hot autumn we are preparing to experience is linked to the virus accompanying our daily lives for 18 months now.

Premise: All the indicators, from the incidence to the hospital beds occupancy, are decreasing. A big difference from a year ago, when the first two weeks of September showed a rapid epidemic growth.

Yet, everyone is worried about the arrival of autumn given schools starting and the resumption of indoor activities. And here is that "hot autumn" returns to make its way into the common lexicon. But what will really happen in the next few weeks? Long-term forecasts are always full of uncertainty, making them is a gamble given the variables that come into play. However, we can say something without fear of being wrong: "this autumn will be different from that of 2020".

It is plausible that the reopening of schools, the full resumption of production activities, and public transport under pressure, will help change the infection trend again this year. However, something has changed. Something substantial has changed. Last year the population was fully susceptible to the virus, unprotected by vaccines. We know how the evolution of the epidemic curve depends on three crucial factors:

1. The average number of contacts of each individual.
2. The probability that an infected person will infect another person by increasing infectivity.
3. The time of infectivity of the disease.

Last year we could only check the first term. And to contain the epidemic, we adopted the closure of activities, which made the curve go down slowly.

With the introduction of vaccines, we can affect the likelihood of infecting and the time of infectivity, that is, how long one remains contagious. A study published in Nature (https://www.nature.com/articles/d41586-021-02187-1) tells us that thanks to vaccines, the infectivity time has been halved, from two to a week, and the probability of infecting is very low. Then, although the Delta is more contagious than the original strains, it has a shorter latency time (the incubation period of the disease in which it is spreadable but without symptoms). From an average of six days, it is now four (https://www.nature.com/articles/d41586-021-01986-w). Thanks to the vaccines, the descent of the curve took place much faster.

So are we out of it? No!

We are in that phase in which it is necessary to understand which of the components driving the epidemic will have the most significant weight. Let's imagine one of those beautiful scales with two plates. On the one hand, the number of contacts per person will increase, with the resumption of productive activities and the school (with everything that revolves around the school). On the other hand, the share of vaccinated people will continue to increase. We move towards the so-called population immunity, significantly reducing the likelihood of getting infected in the vaccinated population (the data already demonstrate this). Which way the scales will hang is early to say, but at least in this hot autumn, we have something to counterbalance the increase in the number of contacts.

And then we always remember that "Unreliable predictions about COVID ‐ 19 infections and hospitalizations make people worry" (www.dx.doi.org/10.1002/jmv.27325)