Covid: infections and immunity, false negative tests, air conditioning risks

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from Laura Della EasterLaura Della Easter

1. Who has been infected, what immunity does he have and how long does it last?

2. Why can a test be negative even if there is an infection?

3. Is air conditioning a risk?

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1. Who has been infected, what immunity does he have and how long does it last?

The infections are increasing exponentially, both due to the loss of efficacy of the vaccine over time and the ability of the variants to neutralize the defenses. The most common question concerns the quality and duration of immunity for those who contracted the virus. Let’s leave the word to the virologist Mauro Pistellodirector of the Virology Operating Unit of the Pisan University Hospital.

How does immunity work in someone who has been infected?

Certainly those who have been infected have enhanced protection. Natural infection is a better immune education system than vaccine. This transfers only part of the information about the virus to the body’s immune system while the disease provides the “complete picture” of Covid. Another factor that is more protected than the vaccine is that it is built to provide coverage against the first strain, that of Wuhan. Those infected now develop immunity against Omicron, thus against an update of the original virus.

How long does immunity from infection last?

The progressive fall in the level of protection following natural infection is slower than the vaccine but precisely due to the fact that these viruses affect the upper airways and therefore we are exposed to them more frequently, sooner or later it may happen that we can reinfect. Normally the level of protection conferred by natural infection is longer than the vaccine, it can last up to a year. Much depends on the individual variables and how similar the circulating virus is to that of the natural infection. If the virus changes rapidly, the protection decreases.

So if natural immunity is more powerful why are we vaccinated?

At the start of the pandemic, vaccinations were needed because the strains were more pathogenic and many people died. The variants are now less dangerous because they affect a population that is largely vaccinated or has been infected. It is a population whose immune systems have been educated. We do not know what would have happened even with Omicron, which today gives us less concern, if there had not been such a widespread vaccination campaign. If the variants do not have a serious impact, it is because we are vaccinated.

Since the variants are not dangerous, does the fourth dose make sense?

In my opinion, if the variants are always these, if the context does not change, it makes sense to vaccinate only the most fragile subjects, because they have an immune system that responds little and therefore are more exposed. I would vaccinate children because you never know and they can act as an infection reservoir. Administration to those who have no problems only in the case of more pathogenic variants but at that point, with modified sera more responsive to the variants. If, in the future, there is a more dangerous variant then everything should be reconsidered.

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2. Why can a test be negative even if there is an infection?

Often those who have been infected are positive only on the second test. How come? “Putting aside the system being used and the operator’s ability to swab, it sometimes happens that the symptoms may anticipate the presence or detectable amount of the virus,” says the virologist Mauro Pistello. «The amount of virus is a sort of curve that tends to rise up to a certain point, after which the immune system takes control of the situation and replication is progressively reduced until it disappears. So if you are in the initial phase it is possible that the swab does not detect it. So much so that it is recommended, especially in symptomatic cases, to do repeated swabs after a few hours or a day or two to be sure of the negativity ».

woman shows arm muscle, confidence, self confidence

3. Is air conditioning a risk?

This is a particularly hot summer. The topic of air conditioning is back, but this time, in addition to the problem of energy consumption, there is the question of whether the devices can be a vehicle for the spread of the virus. Do we really run this risk and how can we make the environment safer? We turned the question over to the virologist Maria Chironna, professor at the University of Bari and head of the Covid analysis laboratory at the Polyclinic. «Unfortunately, the air conditioners used to cool rooms in summer are not air“ purifiers ”. Therefore, the risk is that they can be receptacles for microorganisms as well as for dust, if not subjected to maintenance and regular checks. It is closed environments without air circulation that increase the risk of contagion. Sars-CoV-2 is an airborne virus. Therefore, other systems are needed to facilitate the exchange of air, both in winter and in summer. And this must concern closed public environments, workplaces and means of transport. It is important to make investments in these new technologies for air exchange which would lead to undoubted benefits also for other diseases transmitted by air ».

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