8 March 2022
A new, rather bold study involving health infected volunteers has shown that the severity of symptoms experienced is unrelated to how much virus is shed. In other words, even someone with minimal symptoms can shed and spread the virus a lot.
The bottom line of this is that people should wear masks to stop them spreading the virus.
Here is a cut-down version of the Nature Medicine article in Australian Doctor.
COVID-19 symptom severity ‘no indication’ of viral shedding
A world-first study offers insight into a key public health question about transmission, researchers say
4th April 2022 By Reuters Health
The world’s first ‘human challenge’ trial in which volunteers were deliberately exposed to SARS-CoV-2 has found that symptoms have no effect on how likely an infected person is to pass the infection on to others.
The UK study showed that among the 18 participants who developed COVID-19, the severity of symptoms, or whether they displayed symptoms at all, had nothing to do with the viral load in their airways.
Viral load was measured by a focus-forming assay (FFA) and quantitative polymerase chain reaction (qPCR) in the project led by Imperial College London and contract research company Open Orphan.
“There was no correlation between the amount of viral shedding by qPCR or FFA and symptom score,” the researchers said in Nature Medicine.
“Furthermore, our data clearly show that SARS-CoV-2 viral shedding occurs at high levels irrespective of symptom severity, thus explaining the high transmissibility of this infection and emphasising that symptom severity cannot be considered a surrogate for transmission risk in this disease.”
The trial exposed 36 healthy young adults without a history of infection or vaccination to the original SARS-CoV-2 strain of the virus and monitored them in a quarantined setting.
Since two volunteers were found to have had antibodies against the virus after all, they were excluded from the analysis.
Slightly more than half of them contracted the virus.
No serious adverse events occurred and the human challenge study model was shown to be safe and well tolerated in healthy young adults, the research team had said earlier this year.
“With virus present at significantly higher titres in the nose than the throat, these data provide clear evidence that emphasises the critical importance of wearing face coverings over the nose as well as the mouth,” the study team wrote.
A key unresolved question for public health had been whether transmission was less likely to occur during asymptomatic or mild infection compared to more severe disease, the researchers said.
More information: Nat Med 2022; 31 Mar.