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Volume 5, Issue 10

Determining the impact of vaccination on SARS-CoV-2 RT-PCR cycle threshold values and infectious viral titres Open Access

Abstract

As the COVID-19 pandemic continues, efforts to better understand severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral shedding and transmission in both unvaccinated and vaccinated populations remain critical to informing public health policies and vaccine development. The utility of using real time RT-PCR cycle threshold values (C values) as a proxy for infectious viral litres from individuals infected with SARS-CoV-2 is yet to be fully understood. This retrospective observational cohort study compares quantitative infectious viral litres derived from a focus-forming viral titre assay with SARS-CoV-2 RT-PCR C values in both unvaccinated and vaccinated individuals infected with the Delta strain.

Nasopharyngeal swabs positive for SARS-CoV-2 by RT-PCR with a C value <27 collected from 26 June to 17 October 2021 at the University of Vermont Medical Center Clinical Laboratory for which vaccination records were available were included. Partially vaccinated and individuals <18 years of age were excluded. Infectious viral litres were determined using a micro-focus forming assay under BSL-3 containment.

In total, 119 specimens from 22 unvaccinated and 97 vaccinated individuals met all inclusion criteria and had sufficient residual volume to undergo viral titring. A negative correlation between RT-PCR C values and viral litres was observed in both unvaccinated and vaccinated groups. No difference in mean C value or viral titre was detected between vaccinated and unvaccinated groups. Viral litres did not change as a function of time since vaccination.

Our results add to the growing body of knowledge regarding the correlation of SARS-CoV-2 RNA levels and levels of infectious virus. At similar C values, vaccination does not appear to impact an individual’s potential infectivity when infected with the Delta variant.

  • Received:
  • Accepted:
  • Published Online:
Keyword(s): SARS-CoV-2 , COVID-19 , CT , micro-focus forming assay , RT-qPCR and viral titre
Funding
This study was supported by the:
  • NIH (Award P30GM118228-04)
    • Principle Award Recipient: JessicaW Crothers
  • NIH (Award P20GM113131)
    • Principle Award Recipient: W.Kelley Thomas
  • NIH (Award P20GM103449)
    • Principle Award Recipient: JulieA Dragon
  • NIH (Award P30GM118228-04)
    • Principle Award Recipient: EmilyA Bruce
© 2023 The Authors
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License.
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/content/journal/acmi/10.1099/acmi.0.000597.v3
2023-10-20
2024-05-19
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Determining the impact of vaccination on SARS-CoV-2 RT-PCR cycle threshold values and infectious viral titres
Access Microbiology 5, 000597.v3 (2023); https://doi.org/10.1099/acmi.0.000597.v3
/content/journal/acmi/10.1099/acmi.0.000597.v3
/content/journal/acmi/10.1099/acmi.0.000597.v3
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