tetano
Editor, Senior Moderator
Access Microbiol
. 2023 Oct 20;5(10):000597.v3.
doi: 10.1099/acmi.0.000597.v3. eCollection 2023. Determining the impact of vaccination on SARS-CoV-2 RT-PCR cycle threshold values and infectious viral titres
Katherine L Peterson[SUP] 1 [/SUP], Julia P Snyder[SUP] 2 [/SUP], Hannah W Despres[SUP] 3 [/SUP], Madaline M Schmidt[SUP] 3 [/SUP], Korin M Eckstrom[SUP] 3 [/SUP], Allison L Unger[SUP] 2 [/SUP], Marya P Carmolli[SUP] 3 [/SUP], Joseph L Sevigny[SUP] 4 [/SUP], David J Shirley[SUP] 5 [/SUP], Julie A Dragon[SUP] 3 [/SUP], W Kelley Thomas[SUP] 4 [/SUP], Emily A Bruce[SUP] 3 [/SUP], Jessica W Crothers[SUP] 2 [/SUP]
Affiliations
Background: 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[SUB]T[/SUB] 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[SUB]T[/SUB] values in both unvaccinated and vaccinated individuals infected with the Delta strain.
Methods: Nasopharyngeal swabs positive for SARS-CoV-2 by RT-PCR with a C[SUB]T[/SUB] 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.
Results: 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[SUB]T[/SUB] values and viral litres was observed in both unvaccinated and vaccinated groups. No difference in mean C[SUB]T[/SUB] value or viral titre was detected between vaccinated and unvaccinated groups. Viral litres did not change as a function of time since vaccination.
Conclusions: 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[SUB]T[/SUB] values, vaccination does not appear to impact an individual's potential infectivity when infected with the Delta variant.
Keywords: SARS-CoV-2; COVID-19; CT; RT-qPCR; micro-focus forming assay; viral titre.
. 2023 Oct 20;5(10):000597.v3.
doi: 10.1099/acmi.0.000597.v3. eCollection 2023. Determining the impact of vaccination on SARS-CoV-2 RT-PCR cycle threshold values and infectious viral titres
Katherine L Peterson[SUP] 1 [/SUP], Julia P Snyder[SUP] 2 [/SUP], Hannah W Despres[SUP] 3 [/SUP], Madaline M Schmidt[SUP] 3 [/SUP], Korin M Eckstrom[SUP] 3 [/SUP], Allison L Unger[SUP] 2 [/SUP], Marya P Carmolli[SUP] 3 [/SUP], Joseph L Sevigny[SUP] 4 [/SUP], David J Shirley[SUP] 5 [/SUP], Julie A Dragon[SUP] 3 [/SUP], W Kelley Thomas[SUP] 4 [/SUP], Emily A Bruce[SUP] 3 [/SUP], Jessica W Crothers[SUP] 2 [/SUP]
Affiliations
- PMID: 37970082
- PMCID: PMC10634488
- DOI: 10.1099/acmi.0.000597.v3
Background: 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[SUB]T[/SUB] 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[SUB]T[/SUB] values in both unvaccinated and vaccinated individuals infected with the Delta strain.
Methods: Nasopharyngeal swabs positive for SARS-CoV-2 by RT-PCR with a C[SUB]T[/SUB] 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.
Results: 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[SUB]T[/SUB] values and viral litres was observed in both unvaccinated and vaccinated groups. No difference in mean C[SUB]T[/SUB] value or viral titre was detected between vaccinated and unvaccinated groups. Viral litres did not change as a function of time since vaccination.
Conclusions: 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[SUB]T[/SUB] values, vaccination does not appear to impact an individual's potential infectivity when infected with the Delta variant.
Keywords: SARS-CoV-2; COVID-19; CT; RT-qPCR; micro-focus forming assay; viral titre.