Infectiousness peaks in first five days of COVID-19 symptoms, research suggests

Henrietta Brewer
November 20, 2020

Examining the components of immune memory, the scientists found that that antibodies were "durable" with only "modest declines" emerging at six to eight months.

The five days after a coronavirus-infected individual develops symptoms are when they are at their most infectious, a study has revealed. In stool samples though, the virus can be detected for upto three weeks though these are basically viral fragments and not the whole virus that can cause infection, they added.

Experts collated and scrutinised 98 papers to inform their conclusions.

In the research, the scientists specifically looked at people infected with SARS-CoV-2 and mainly those who were hospitalised.

Shedding of the SARS-CoV-2 virus has been one of the areas of intense research from the start of the pandemic to understand the dynamics of the disease transmission in order to limit its spread.


Study co-author, Dr Christoph Neumann-Haefelin, Head of the Gerok Liver Center at University Hospital Freiburg, also expressed optimism about their results, suggesting that immunity against the new coronavirus can be achieved after an infection, and that, "similarly, vaccines now being tested in trials could provide significant protection against SARS-CoV-2".

Eight of 13 studies examining viral load in upper respiratory tract samples showed peak viral load within the first week of symptom onset, with the highest viral loads reported "soon or after" symptom onset, or day 3 to 5 of illness.

In contrast, the viral loads of SARS and MERS-CoV peaked at 10-14 days and 7-10 days after symptom onset, respectively. The upper respiratory tract is believed to be the main source of transmission since COVID-19 is largely spread through particles that enter the air.

"These so-called memory T-cells after SARS-CoV-2 infection look similar to those after a real flu", said study co-author Dr Maike Hofmann, a scientist at the Department of Medicine II at the Medical Center - University of Freiburg.

A Portuguese study found that in the more than the 300 coronavirus patients examined, the antibody response was the strongest in the first three weeks after symptoms.


Researchers say delirium can be particularly detrimental to elderly people, increasing their likelihood of severe disease and death.

There were 79 studies, with a total of 5,340 patients, with 58 studies in China, and 73 studies including hospitalized patients only. The researchers found genetic evidence of the virus in diaphragm muscle cells in some of those who died from COVID-19, and microscopy analyses showed much more connective tissue scarring (fibrosis) in COVID-19 patients' diaphragms, indicating damage, study coauthor Coen Ottenheijm told Reuters.

People who contract the new coronavirus are most likely to be highly infectious for nine days after the onset of symptoms, a new study has found, reinforcing the need for self-isolation for at least 10 days.

Many countries recommend that people with the virus should self-isolate for 10 days, which the authors said is in line with their findings, cautiously covering the period of infectiousness.

From these studies, the authors calculated the average length of viral RNA shedding and examined the changes in viral load and the success of isolating the live virus from different samples collected throughout an infection.


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