Science

Coronavirus, what do we know about transmission from people without symptoms?

It would not be the main route of transmission of the virus, according to institutional sources. But we continue to talk about their role in feeding the pandemic, from several fronts

coronavirus
(photo: Martin Sanchez on Unsplash)

In an atmosphere of emergency , in front of the arrival of a new pathogen, unknown before, uncertainty is in some way physiological, to a certain extent it is also in communication. One of the most discussed aspects related to the new coronavirus is for example the contagiousness or less of the asymptomatic subjects or with few symptoms (pauci-symptomatic) . And it is also one of the fundamental aspects in light of the containment policies of the pandemic (like the issue of tampons). Even in the climate of uncertainty, some answers regarding the infectivity of asymptomatic subjects or paucisintomatici comes from many places. We tried to put them together.

Let's start from the official statements, the institutional ones. The same that could however be reviewed in the light of the latest discoveries. In fact, the same methods of transmission of the virus are a matter of discussion for these hours: some studies would suggest the capacity of the virus to reach greater distances than previously believed, by virtue of the potential to propagate also through aerosol and not only droplets (a distinction in substance of dimensions, smaller for the aerosol). At the moment, however, the European Center for Disease Prevention and Control (Ecdc), recalls that the main route of transmission of the virus is through the droplets of saliva emitted while coughing or sneezing, by those who therefore show symptoms of the infection from coronavirus. But not only: some evidences, write from the ECDC, “suggest that the transmission may also take place by an infected person two days before he manifests the symptoms; however, uncertainty remains about the effects of transmission from non-symptomatic people “.

The World Health Organization basically reiterates the same things: the main routes of transmission are from infected people who show the symptoms , in known ways, and that “ The risk of contracting Covid- 19 by someone without any symptoms it is rather low “. Rather low does not mean null , and again: the distinction on the risk of contagiousness should also refer to the presence of few symptoms . And in fact they add: “Many people with Covid – 19 have only mild symptoms. Especially at the beginning of the disease. For this it is possible to get sick of Covid – 19 from someone who has, for example, just a weak cough and you don't feel sick “. And perhaps much of the confusion , as well as dell uncertainty on the subject has to do with this typology-intensity of symptoms rather than total absence, as well as with the notification and the definition itself that over time has had for symptomatic cases and asymptomatic , notes the New York Times .

The official positions summarize the evidence on the matter, and are open to continuous updates which could come from continuing scientific research on the subject. Something in this sense begins to arrive, together with some anecdotal observations , or still not completely confirmed by the scientific community. Reason why it happens – and it happens – to hear completely discordant voices on the subject even by experts. What did they say?

The Harvard University epidemiologist Eric Feigl-Ding , commenting on the data coming from South Korea, he warned for example about the risk posed by young people as vectors of the disease: precisely because they are unaware (of the symptoms) with their behavior could fuel the spread of the virus.

Also the analyzes conducted in Vo 'Euganeo (Veneto) have shown that about 70% of the infected population is asymptomatic. Subjects identified as healthy carriers , but still carriers, carriers, ” formidable sources of contagion “, and therefore dutifully to be isolated. The isolation of the positive cases in Vo 'Euganeo himself, and therefore the rapid fall of the cases, would have confirmed the appeal launched by some experts. Other preliminary analyzes, conducted in Lombardia , and for now only available in pre-print on arXiv , for example, they let us suppose similar potential of transmission for people with or without symptoms, since no significant differences were detected between the nasal swabs of people with or without symptoms in viral loads , despite all the limitations relating to the reduced number of cases analyzed. Of the same opinion, a communication that appeared in recent days on the pages of the New England Journal of Medicine. But there are now several cases that on the whole suggest an transmission from asymptomatic or before the onset of symptoms, from presymptomatic cases . In this regard, however, again from the ECDC in the seventh update of the Rapid risk assessment, they write what weight this has on the transmission dynamics of the pandemic is unclear, also because the evidence is not optimal, they explain. They certainly continue to accumulate, also as regards the mild symptoms . Just a couple of days ago for example a small study published on Nature, conducted on 9 patients, showed how, even in cases from Covid – 19 with Mild symptoms, a high rate of replication and spread of the virus in the upper airways was observed in the first week of symptoms .

But still: just a few hours ago the virologist at the head of Centers for Disease Prevention and Control (Cdc) , Robert Redfield , in an interview spoke about the role of asymptomatic as disease vectors, as one of the data emerging from the analysis of the data on the subject. Up to 25%, Redfield explained, they could be asymptomatic : “is an important fact, because there are individuals which may have no symptoms and which contribute to the transmission, and we have learned that they actually contribute to the transmission “, writes National Public Radio. This, together with evidence that up to 48 hours before the appearance of the symptoms – in whom they will arise – considerable quantities of viruses are observed at the oropharyngeal level, it would explain the rapid spread of the virus in the country, he said.

And it could also lead to revisions on the recommendations for use of the masks . The CoC at the moment, as well as the WHO, recommend their use – according to correct hygiene measures – only to those who are sick or take care of sick people, outside of hospital settings. And the same Cdc which is headed by Redfield when asked if the transmission of the virus can also take place by people not sick people respond in the same tone as the statements of the ECDC and WHO are at the moment: you are more contagious when you are sicker and even admitting a transmission before the onset of symptoms, this is not currently believed to be the preferred route for the virus to spread. But there is no lack of rumors that, writes the Cnn , these statements they should at least be reviewed.

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