Covid: asymptomatic people are more and more dangerous in the contagion chain

A study found that 59% of new cases of coronavirus comes from infections by “asymptomatic transmission”. A 35% of new infections affect people who do not yet have symptoms (presymptomatic) and one 24% who have never had one.

The analytical model just published by JAMA Network Open medical journal, highlights how the transmission of people without symptoms accounts for more than half of all cases, according to the Spanish scientific press agency Sinc.

As the Covid-19 has started to spread around the world, scientists observed that, unlike the coronavirus that caused the 2003 epidemic, the spread of SARS-CoV-2 it could not be contained by screening based solely on symptoms. According to previous scientific publications, asymptomatic and clinically mild infections were rare in SARS-CoV 2003.

In addition, no cases of transmission were reported prior to symptom onset. However, the new coronavirus (Covid-19) has spread faster than the previous one and tests “have shown that it is transmitted by people without symptoms”.

Coronavirus: they create an application that detects the asymptomatic by coughing

That is why it was concluded that the identification and isolation only of individuals showing symptoms of Covid-19, “would not be able to control the spread current pandemic ”, but the exact proportion of infections in these patients was lacking.

Research now published in the monthly journal of the American Medical Association suggests that transmission from infected people but what has no symptoms may result from two different infection states: people presymptomatic (which are infectious before symptoms appear) and people who never have symptoms (asymptomatic or never symptomatic infections).

Experts analyzed the relative amount of contagion of presymptomatic patients, never symptomatic and symptomatic in different contexts in which the proportion of transmission from people who never develop symptoms (i.e. remain asymptomatic) and the infectious period vary according to best published estimates.

The basic assumption of the model was that the maximum infectivity occurs in the median of symptom onset, as the 30% of those infected never develop and that 75% are as contagious as those who develop symptoms. Combined, these basic assumptions imply that infected people who never develop symptoms may account for 24% of all transmissions.

70-year-old woman, asymptomatic for three months, another coronavirus mystery

Thus, the results show how the 59% of all transmissions are from asymptomatic transmission, according to the model’s baseline scenario. In contrast, 35% of new cases come from people who infect other people before showing symptoms (presymptomatic individuals); and 24% of people who do not develop any of the symptoms.

“Under a wide range of values ​​for each of these assumptions, it is estimated that at least 50% of new SARS-CoV-2 infections come from exposure to people who are infected but without symptoms”, State Scientists from the Centers for Disease Control and Prevention (CDC) in Atlanta (USA).

Its authors state that in addition to identifying and isolating people with symptomatic Covid-19, “to effectively control the spread, it will be necessary reduce the risk of transmission from infected people who have no symptoms“.

“Measures like use of masks, hand hygiene, social distancing and the strategic tests people who are not sick will be essential to slow the spread disease, up to safe and effective vaccines and that these are widely used, ”they concluded.

EuDr / MC