A study co-authored by UMass Chan researchers shows a significant difference in the infectivity of SARS-CoV-2.

Recent studies by UMass Chan researchers and collaborators from several institutions show that there are large variations in SARS-CoV-2 levels and infectivity among people in the early stages of COVID-19. It may be an explanation of the phenomenon of “super spreader”.Was announced in Nature microbiology ..

This study provides a detailed view of SARS-CoV-2 infection through continuous virus testing by several methods, including PCR testing, antigen testing, and virus culture to measure viral replication.

Nasal and saliva samples were taken from 60 asymptomatic or mildly symptomatic COVID-19 students at the University of Illinois at Urbana-Champaign between late 2020 and early 2021. Participants received new positive PCR results within the last 24 hours or were exposed to someone with COVID-19 within the last 5 days. This study was supported by the National Institutes of Health’s Rapid Acceleration of Diagnosis (RADx) initiative.

The term super-spreader refers to infected individuals who make up the majority of SARS-CoV-2 infections.

“Until this study, it wasn’t fully explained why some people seemed to infect the virus more extensively than others,” co-author Laura L. Gibson, MD (UMass). Chan’s associate professor) said. Dr. Gibson was previously a co-leader of RADx Clinical Studies Core. Richard M. Hydak, Professor of Medicine And a medical chair and professor.

Based on the results of the study, Gibson said that COVID-19 appears to be similar to most other infections, some people get sick and some do not get the same infection. Said. This clinical variability depends on many factors, including differences between pathogens, individual differences in immune responses, and even the location of the virus in the oral cavity or nasal passages.

The current study was conducted on individuals with unknown SARS-CoV-2 immunity. No one was vaccinated with COVID-19 because they had never been infected before and research was done before the vaccine became widespread.

Researchers measured the dynamics of the SARS-CoV-2 virus in several ways by sampling participants daily for up to 14 days.

First, they test the nostrils using a sample from one nostril for a PCR test to detect whether the virus is dead or alive, and the other for an antigen test to detect viral proteins. The sample was tested through the nostrils. PCR nasal samples were also tested in virus cultures. This is a laboratory analysis that detects viruses that are alive and replicating and can spread to the next person.

“A unique aspect of this approach was to use several test modalities on samples obtained on the same day and repeat those measurements daily throughout the course of SARS-CoV-2 infection,” Gibson said. explained.

To analyze the data from these samples, researchers used mathematical models to map the longitudinal dynamics of viral shedding based on PCR tests performed during the course of infection and data from virus cultures. bottom. The model described not only virus spread and clearance, but also patterns of virus shedding. It generally indicates infectious activity when the virus is released from the body.

“Daily sampling of participants provided robust detailed data for this modeling,” Gibson said. “There is a great deal of individual variation in virus infectivity, and it turns out that such heterogeneity is likely to depend not only on viral factors but also on human factors, supporting the idea of ​​super-spreaders. rice field.”

Researchers also compared the PCR test results of saliva and nasal samples and found that there was a surprising difference between the two anatomical positions, even though they were connected behind the throat. .. “Approximately 85% of participants had the virus detected in saliva at least one day before the nasal sample,” Gibson said.

The authors of the paper did not suggest that saliva testing is superior to nasal testing. Nose sample. However, there are many caveats to that approach, and people need to use diagnostic tests only with the specific sample type in which they were designed. “

The study was conducted when alpha and previous mutants were circulating, but the researchers did not see any difference in viral dynamics based on the mutants evaluated in this study, so the general conclusion is probably other. Gibson said it would also apply to variants of.

In addition, the study found differences between participants that were not well explained by the results of the virus test, Gibson said. “The overall finding was that no matter how the virus was tested, the amount or duration of the virus in the sample varied from person to person, and not all variations were explained by virus measurements. Factors (eg, nasal SARS-CoV-2 antibody levels) are probably important and can be measured as a clinical tool. “

Other UMass Chan School of Medicine researchers who have authored papers with researchers from the University of Illinois at Urbana Champaign, John’s Hopkins School of Medicine, and the National Institute of Biomedical Imaging and Biological Engineering are: John P. Broach, MD, MPH, MBA, Associate Professor of Emergency Medicine. Dr. Bruce A. Burton, Professor of Population and Quantitative Health Sciences. Peter Lazar, application database developer. And Dr. McManus.

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