The risk of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be assessed by determining the time course of dissemination using diagnostic indicators such as cycle threshold (Ct) values through recovery of SARS-CoV-2 from viral culture. and reverse transcriptase polymerase chain reaction (RT-PCR) tests.
Based on previous studies, RT-PCR results remained positive for up to 4 weeks after people infected with SARS-CoV-2 developed symptoms. However, recovery of viable virus could not occur ten days after the initial positive test. Vaccinated individuals infected with the Delta variant were found to have similar Ct values but lower viral titers compared with unvaccinated individuals. However, such investigations involved recruiting participants at or shortly after symptom onset, which limits their description of viral shedding during the presymptomatic period.
A new study from the Centers for Disease Control and Prevention (CDC) published in the journal Vaccine aimed to analyze the viral shedding and conversion timeline of people infected with SARS-CoV-2 from exposure to infection and the onset of symptoms during a Delta outbreak period in a federal prison in Texas.
Brief communication: Viral excretion of SARS-CoV-2 in vaccinated and unvaccinated persons: a case series. Image Credit: NIAID
About the study
The study involved the collection of nasal swabs from incarcerated individuals for reverse transcription polymerase chain reaction (RT-PCR) and antigen testing every other day after exposure. The exposed people were transferred to quarantine. Those with positive antigen tests were transferred to medical isolation. A single swab was collected from infected persons daily for ten days and analyzed by viral culture and RT-PCR. After ten days, all infected participants were required to complete a symptom questionnaire.
Information on previous medical history, demographic characteristics, history of previous SARS-CoV-2 infection, and vaccination status of all participants was obtained. Viral culture was performed on days 0, 3, 5, 7, and 9 after the first positive test with Vero-E6 cells. The incubation of the infected cells with the sample took place at 37 Cin 5% CO2 and the cytopathic effect was observed. If the cytopathic effect was observed, it was defined as isolated virus; if no cytopathic effect was observed, it was defined as non-isolated virus.
Study findings
A total of 12 people were identified as eligible for this case series analysis. All were male and all identified as non-Hispanic white. The median age was reported to be 43 years. Of 12 participants, 3 never had a positive antigen test. Of the 9 participants with positive antigen tests, 5 had positive viral culture results from samples collected on the same day as the positive antigen test, while 2 had positive viral culture results but a negative antigen test on the same day.
Ten participants were reported to have completed a primary vaccination series against COVID-19 prior to the outbreak. Among them, 2 had a previous SARS-CoV-2 infection and were reported to have been vaccinated afterwards. SARS-CoV-2 was recovered in viral culture from 9 participants for a median duration of 6 days. SARS-CoV-2 RNA was detected in all 12 participants. In addition, cycle threshold values were observed to increase with the number of days from the date of the first positive test. Samples with positive culture results showed lower Ct values than those with negative culture results.
Eleven participants reported at least one underlying medical condition, with being overweight and a history of tobacco use disorder the most common. Information on symptoms was available for 10 participants, of whom 4 were asymptomatic. However, 3 of these 4 participants had at least one positive viral culture result after the first positive RT-PCR. The median duration of symptom onset was reported to be 7 days. Among the participants who reported symptoms, 3 had positive viral culture results and a positive RT-PCR test before symptom onset.
Therefore, the current study indicated that both vaccinated and unvaccinated people were capable of transmitting SARS-CoV-2. The results of this study suggest that transmission occurs early after infection and before the onset of symptoms. They also highlight the need for non-pharmaceutical interventions to reduce SARS-CoV-2 transmission in high-transmission settings. Further research is required to understand the extent to which vaccinated persons with SARS-CoV-2 infection can infect others and to correlate viral shedding with disease between vaccinated and unvaccinated persons.
limitations
There are some limitations in the study. First, this study is limited to infections caused by the Delta variant of the virus, which might behave differently from other variants. Second, vaccinated and unvaccinated individuals were not directly compared. A third limitation of the study is that it cannot be generalized to settings with low vaccination rates and different transmission dynamics. Fourth, recovery of SARS-CoV-2 in viral culture may not predict SARS-CoV-2 transmissibility. Finally, antigen-positive results could not be correlated with infectivity throughout the disease.
Source: news.google.com