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article imageAsymptomatic carriers of COVID-19 still risk lung damage

By Tim Sandle     Jul 14, 2020 in Science
It's established that many people infected with coronavirus are 'asymptomatic'. While these people can spread the virus, the virus isn't actually harming them, right? Not so says a new study published in Nature.
Someone who is infected with the SARS-CoV-2 virus and remains asymptomatic, that is free of coughing, fever, fatigue and other common signs of infection, can still be adversely affected by the infection. A new study reveals that virus will still be causing some harm to their lungs. This may be mild and it may be reversible, but the effects will vary between different individuals.
The study, published in Nature Medicine, reveals a high rate of minor lung inflammation in many individuals who exhibit no outward symptoms of coronavirus. See: "Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections."
This is significant because asymptomatic carriers of coronaviruses are under-studied and it is unclear just how many people are asymptomatic carriers of SARS-CoV-2. At present, the proportion of the population could be anywhere between 30 and 45 percent. Importantly, some models estimate that around 40 percent of transmission comes from asymptomatic cases.
The importance of understanding what asymptomatic means is brought to light by researchers studying the spread of the SARS-CoV-2 virus between healthcare workers. The scientists have found high levels of asymptomatic infections during the peak of the pandemic in London. These results, published as part of correspondence in the medical journal The Lancet, highlight the importance of routinely screening healthcare staff for the virus to protect frontline workers and their patients.
The data is composed of twice-weekly self-administered nose and throat swabs together with monthly blood samples (assessed using high-sensitivity serology assays), taken from 200 frontline healthcare staff.
What is of interest is that 45 percent of healthcare staff (from a sampled population of 200 people) showed evidence of having been infected with the coronavirus within a month of testing having started (which shows how the virus can spread within a highly populated, indoor environment like a hospital). Of significance is the finding that 38 percent of infections were not associated with symptoms within 7 days of a positive sample being recorded.
The study reference is: "Pandemic peak SARS-CoV-2 infection and seroconversion rates in London frontline health-care workers."
While some analysts downplay the asymptomatic variables as less important than seeking to achieve herd immunity, there is no consensus upon what herd immunity actually means. This relates to defining the herd immunity threshold, which is the proportion of a population that need to be immune in order for an infectious disease to become stable in that community.
For instance, the herd immunity threshold depends on how many people each infected person actually infects — a number that can vary by location. In an article for Quanta Magazine, Kevin Hartnett presents some interesting mathematics exploring just how complex herd immunity is to define and to measure. See: "The Tricky Math of Herd Immunity for COVID-19."
More about asymptomatic, Lung damage, Covid19, coronavirus
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