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Proportion of asymptomatic coronavirus carriers above 70 percent

Is it best to test more people for coronavirus using less accurate tests or to test fewer people with more accurate tests? This is one of the conundrums arising from our latest research round-up. We also look at just how many in the population are likely to be asymptomatic carriers and also how many people are likely to have been infected.

COVID-19 pathophysiology

The probability of symptoms and critical disease after SARS-CoV-2 infection have been quantified, according to a new study. The researchers quantified the probability of developing symptoms and the chance of these leading to the occurrence of a critical disease (defined as one requiring intensive care or resulting in death), in relation to SARS-CoV-2 positive subjects.

With the study, some 5,484 contacts of SARS-CoV-2 index cases detected in Lombardy, Italy were reviewed, and the positive subjects were identified via nasal swabs and serological assays. It was found that 73.9 percent of the infected individuals (aged less than 60 years) did not develop symptoms, showing the proportion of the population who are asymptomatic. However, the risk of developing symptoms increased with age. Also rising with age was the risk of serious illness, with 6.6 percent of infected subjects older than 60 years going on to develop a critical disease. Finally, the study affirmed earlier findings, indicating that males are at significantly higher risk of suffering with a serious COVID-19 related illness.

The research is titled “Probability of symptoms and critical disease after SARS-CoV-2 infection.”

To look further into these types of observations, a new study has been instigated into the long-term health impacts of COVID-19. This is being led by the U.K. Research and Innovation and the National Institute for Health Research. These bodies have announced that £8.4 million ($11 million) of funding has been allocated for one of the world’s largest studies into the long-term physical and mental health impacts of coronavirus on hospitalised patients.

Mask-wearing is not common in Australia and has not been part of the country's COVID-19 respon...

Mask-wearing is not common in Australia and has not been part of the country's COVID-19 response until recently
William WEST, AFP

Challenges of herd immunity

A new study looking at SARS-CoV-2 seroprevalence in COVID-19 hotspots has been running, as reported in The Lancet. The study considers the first SARS-CoV-2 seroprevalence studies from COVID-19 hotspots in China, the USA, Switzerland, and Spain. The key finding from these representative reviews is that most of the population appears to have remained unexposed to SARS-CoV-2, even in areas with widespread virus circulation. This means most populous areas are far away from reaching natural herd immunity in the population.

Britain is one of a number of countries conducting vaccine trials for COVID-19

Britain is one of a number of countries conducting vaccine trials for COVID-19
BEN STANSALL, AFP

How to test and when to test

Test sensitivity should be secondary to frequency and turnaround time for COVID-19 surveillance, according to a new study. In the study the authors modelled surveillance effectiveness considering test sensitivities, frequency, and sample-to-answer reporting time. The researchers concluded that coronavirus surveillance testing should prioritize accessibility, frequency, and sample-to-answer time. These factors should come above analytical limits of detection, which should be secondary. This is based on a review of data that makes the case for as much testing as possible, ideally of the same people, in order to build up a picture of a given population as rapidly as possible.

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Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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