Researchers are investigating viral shedding in a phase 1, open-label, first-in-human SARS-CoV-2 experimental infection study

In a recent study posted on lancet microberesearchers investigated the release of viral particles into the environment and air after human infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Study: SARS-CoV-2 viral shedding into the air and environment after human infection: a phase 1, open-label, first-in-human study. Image credit: Kateryna Kon/
Study: SARS-CoV-2 viral shedding into the air and environment after human infection: a phase 1, open-label, first-in-human study. Image credit: Kateryna Kon/


To implement effective strategies to reduce transmission of SARS-CoV-2, it is important to understand the transmissibility and timing of transmission. Measurement of viral shedding may be an accurate technique for determining the likelihood of future infection and discovering potential pathways, rather than relying solely on viral load from upper respiratory swabs. . This study aimed to observe the correlation between viral shedding, symptoms over time, and viral load in the upper respiratory tract of individuals infected with SARS-CoV-2.

About research

The team recruited healthy adults aged 18 to 30 who had not been vaccinated and had no history of SARS-CoV-2 infection. The study was conducted at a single center in London and was the first experimental infection study in humans. Participants were tested seronegative and quarantined at the Royal Free London NHS Foundation Trust. The QCOVID tool was utilized to independently estimate the absolute risk of hospitalization and death. We identified participants who exceeded a pre-set risk threshold. Prior to inoculation, patients underwent echocardiography and chest radiography.

Participants were placed in individual negative pressure rooms. This study involved administering 10-50% tissue culture infectious dose (TCID50) of pre-alpha wild-type SARS-CoV-2 to participants via nasal spray. Participants were quarantined for at least 14 days after vaccination until discharge criteria were met. Nose and throat swab collections were performed daily. In this study, air samples were also collected from a distance of 1 meter from the participants’ heads.

Collection of environmental surfaces and wipes was conducted daily. Virological analysis was performed on all samples in this study, including nose and throat samples, mask, air, and environmental samples. The polymerase chain reaction (PCR) was used to quantify the human housekeeping gene 18S ribosomal ribonucleic acid (rRNA) in all samples to determine the impact of sampling efficiency or to estimate total particle shedding for observations. Did. Symptom scores were collected three times daily using a self-reported symptom diary.

The primary outcome of this study was to investigate environmental and air pollution in healthy adults participating in a SARS-CoV-2 human attack model. Methods used for this study included exhaled breath sampling, air sampling, and surface wiping. As a secondary outcome, the study also describes the SARS-CoV-2 transmission pathway and the link between host factors and viral shedding.


The study enrolled 36 participants from 6 March to 8 July 2021. Of the 34 seronegative participants, 18 reported SARS-CoV-2 infection after challenge. Infected participants experienced mild to moderate symptoms and had high viral loads in the nose and throat for prolonged periods after a short incubation period. There was no viral contamination in the air, exhaled breath, or rooms of uninfected individuals. The study also found that all 18 infected participants released virus-laden particles into the air.

Viral contamination was found to be consistent across the five wiped surfaces. The study found that viable SARS-CoV-2 was detected in 16 masks and 13 surface swabs, but not in hand samples or Coriolis air samples.

In this study, correlation analyzes were performed on all samples collected from participants to examine the relationship between viral shedding and viral load in swabs and symptoms. Surface and airborne viral load measurements were found to be clustered together. The hand and mask viral load clustered with the nasal viral load. Hand swabs showed a strong association with TV remote controls and bathroom handles. Nasal viral load correlated more strongly with mask, hand, air, and surface viral load than with throat viral load. Notably, shedding and symptom scores showed minimal correlation.

Consistent levels of the human housekeeping gene 18S rRNA were found in daily air samples taken from the same individual. This suggests that the amount of air particles emitted during infection did not change and that particles detected in air samples remained stable. The difference in his 18S rRNA from the mask is more pronounced, and this type of sampling is more variable, depending on various factors such as the individual’s activity level, exhalation events, or mask placement during the 1-h sampling period. Indicates that you may be affected.

Viral RNA was identified from masks, air, and surface swabs prior to the onset of reported symptoms. Viral RNA release accounted for 2%, 8%, 9%, and 10% of the total area under the curve (AUC) for hand swab, surface swab, air, and mask release, respectively. The study also found that only 7% of environmental and air emissions occurred before symptoms were first reported, so the majority of infectivity was first reported as ill health in participants. It also showed that it was detected after


The study found significant amounts of viral contamination in the surrounding environment and air after healthy individuals were infected with SARS-CoV-2. Contamination was found to be extensive but variable and likely of nasal epithelial origin. Since viral shedding occurred after participants reported early symptoms and had a positive lateral flow antigen test (LFT), it is possible that most of the infectivity can be detected by early symptoms that initiate self-testing. .

The correlation between viral shedding and viral load was found to be stronger in the nose compared to the throat, suggesting that infected nasal mucosa is an important viral source for viral transmission.

The research team noted that LFT may be a more effective method for identifying infected people compared to fever screening because of its rapid results. The study concludes that hand hygiene and surface cleaning play an important role in reducing infection risk.

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