New Study on Viral Load-ScienceDaily

According to the reproduction number (R 0), people infected with SARS-CoV-2 spread the infection to an average of 3 to 5 people. While this is a useful indicator in epidemiological settings, “R 0” does not help estimate the risk of infection at the individual or group level. When normal social and environmental factors are removed from the equation, individuals can differ significantly in terms of infectivity and the length of time they actively release the virus.

To better understand and estimate the infectivity of a particular group of individuals, a team led by Dr. Christian Drosten, director of the Institute for Viral Sciences in Charité and a researcher at the German Center for Infection Research (DZIF), said: 25,000 COVID-19 cases to determine viral load. The viral load of a sample (the total number of copies of the SARS-CoV-2 genome contained in the sample) is a useful indicator as it provides an estimate of the amount of virus present in the patient’s throat. Infectivity of an individual. To further improve the estimates, the researchers also applied findings on the minimum viral load threshold normally required to successfully isolate SARS-CoV-2 in cell culture (isolation is infectious). Indicates the presence of a virus). Sequential samples were available for more than 4,300 cases investigated. Using these, by tracking viral load data in the throat over time, researchers were able to model the typical outbreak of viral load during the course of infection. Researchers then looked for significant differences in the data, especially in relation to different age groups, disease severity, and viral mutations.

No significant differences in viral load levels were recorded between SARS-CoV-2 positive individuals aged 20-65 years. The average pharyngeal swab sample contains approximately 2.5 million copies of the SARS-CoV-2 genome. The viral load was found to be lowest in very young children (0-5 years old). Levels began at about 800,000 copies of the viral genome and increased with age, approaching adult levels in older children and adolescents.

“These numbers look very different at first glance, but it’s important to remember that viral load results are shown on a logarithmic scale,” says Professor Drosten. “In fact, the difference in viral load seen in the youngest children is just below the thresholds that are usually considered clinically relevant. Importantly, understand how to reach these values. However, this must be taken into account in the interpretation. They. “Virologists emphasize the difference in sample collection methods between children and adults, adding: “Children’s swabs are significantly smaller in size, less than half the sample volume commonly available in PCR tests. In addition, the level of discomfort associated with the procedure, that is, deep nasopharyngeal swabs, are often replaced by simple throat swabs. Yes, this further reduces the amount of viral material collected. Therefore, in children, it is fully expected that the same level of viral replication will result in lower viral load results. PCR test. “

Comparing the peak viral load of laboratory samples, researchers estimated that the level of infectivity in the youngest children (0-5 years) was about 80% of the infectivity found in adults. As before, it turns out that the values ​​of school-age children and adolescents are closer to those of adults. “This shows that viral load is not directly proportional to infectivity and cannot be converted directly,” explains Professor Drosten. He adds: “Even the infectivity estimates in these databases need to be revised upwards due to the different methods of sampling used in children. These are all part of the overall assessment of clinical virologists. Almost the same level of infectivity has been identified in both this and other studies. “

Symptom-based comparisons confirmed previous observations in cases of COVID-19. This means that even asymptomatic individuals can have very high viral loads. Individuals who needed hospitalization were found to have higher viral loads than others throughout the course of their illness. Researchers have found that individuals infected with SARS-CoV-2 reach peak levels of viral load in their throat 1-3 days before the onset of symptoms, based on a new model of viral load over time. I’m estimating.

Approximately 9% of the COVID-19 cases tested showed very high viral load of over 1 billion copies per sample. More than one-third of these potentially infectious individuals had no or only mild symptoms. “These data provide a virological basis for the notion that a small number of infected people cause the majority of all infections,” explains Professor Drosten. “The fact that this includes a large number of people with no associated symptoms underscores the importance of pandemic measures such as social distance and forced masking.”

Samples collected from individuals infected with the B.1.1.7 (“UK” or “UK”) variant have a 10-fold increase in mean viral load and a laboratory-based estimate of infectivity of 1. It turns out that it has doubled. Of 2.6. To reach these data, researchers obtained viral load data for approximately 1,500 cases infected with B.1.1.7 and infected the same test center, outpatient department, and other clinically tested variants. We compared it with the data of about 1,000 people. Ward at about the same time. Professor Drosten adds: “Laboratory studies may not yet be in a position to provide a clear explanation, but one thing is clear. B.1.1.7 is more infectious than other variants.”

Researchers plan to continue research on viral load throughout the pandemic process. They want to gain insight into the changes that occur when new mutants develop as the virus adapts to elevated levels of herd immunity.

About research

This study was written by scientists at Charité-Universitätsmedizin Berlin, German Center for Infectious Diseases, Cambridge University, Norwegian Institute for Public Health, University of Oslo, Labor Berlin-Charité Vivantes GmbH, Christian-Albrechts-University of. Kiel, and Dr. Labor. Krause and colleague MVZ GmbH.