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Association Between Cycle Threshold Value and Vaccination Status Among Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant Cases in Ontario, Canada, in December 2021

Association Between Cycle Threshold Value and Vaccination Status Among Severe Acute Respiratory... BackgroundIncreased immune evasion by emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and occurrence of breakthrough infections raise questions about whether coronavirus disease 2019 vaccination status affects SARS-CoV-2 viral load among those infected. This study examined the relationship between cycle threshold (Ct) value, which is inversely associated with viral load, and vaccination status at the onset of the Omicron wave onset in Ontario, Canada.MethodsUsing linked provincial databases, we compared median Ct values across vaccination status among polymerase chain reaction–confirmed Omicron variant SARS-CoV-2 cases (sublineages B.1.1.529, BA.1, and BA.1.1) between 6 and 30 December 2021. Cases were presumed to be Omicron based on S-gene target failure. We estimated the relationship between vaccination status and Ct values using multiple linear regression, adjusting for age group, sex, and symptom status.ResultsOf the 27 029 presumed Omicron cases in Ontario, the majority were in individuals who had received a complete vaccine series (87.7%), followed by unvaccinated individuals (8.1%), and those who had received a booster dose (4.2%). The median Ct value for post–booster dose individuals (18.3 [interquartile range, 15.4–22.3]) was significantly higher than that for unvaccinated (17.9 [15.2–21.6]; P = .02) and post–vaccine series individuals (17.8 [15.3–21.5]; P = .005). Post–booster dose cases remained associated with a significantly higher median Ct value than cases in unvaccinated individuals (P ≤ .001), after adjustment for covariates. Compared with values in persons aged 18–29 years, Ct values were significantly lower among most age groups >50 years.ConclusionsWhile slightly lower Ct values were observed among unvaccinated individuals infected with Omicron compared with post–booster dose cases, further research is required to determine whether a significant difference in secondary transmission exists between these groups. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Open Forum Infectious Diseases Oxford University Press

Association Between Cycle Threshold Value and Vaccination Status Among Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant Cases in Ontario, Canada, in December 2021

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Publisher
Oxford University Press
Copyright
© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.
eISSN
2328-8957
DOI
10.1093/ofid/ofad282
Publisher site
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Abstract

BackgroundIncreased immune evasion by emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and occurrence of breakthrough infections raise questions about whether coronavirus disease 2019 vaccination status affects SARS-CoV-2 viral load among those infected. This study examined the relationship between cycle threshold (Ct) value, which is inversely associated with viral load, and vaccination status at the onset of the Omicron wave onset in Ontario, Canada.MethodsUsing linked provincial databases, we compared median Ct values across vaccination status among polymerase chain reaction–confirmed Omicron variant SARS-CoV-2 cases (sublineages B.1.1.529, BA.1, and BA.1.1) between 6 and 30 December 2021. Cases were presumed to be Omicron based on S-gene target failure. We estimated the relationship between vaccination status and Ct values using multiple linear regression, adjusting for age group, sex, and symptom status.ResultsOf the 27 029 presumed Omicron cases in Ontario, the majority were in individuals who had received a complete vaccine series (87.7%), followed by unvaccinated individuals (8.1%), and those who had received a booster dose (4.2%). The median Ct value for post–booster dose individuals (18.3 [interquartile range, 15.4–22.3]) was significantly higher than that for unvaccinated (17.9 [15.2–21.6]; P = .02) and post–vaccine series individuals (17.8 [15.3–21.5]; P = .005). Post–booster dose cases remained associated with a significantly higher median Ct value than cases in unvaccinated individuals (P ≤ .001), after adjustment for covariates. Compared with values in persons aged 18–29 years, Ct values were significantly lower among most age groups >50 years.ConclusionsWhile slightly lower Ct values were observed among unvaccinated individuals infected with Omicron compared with post–booster dose cases, further research is required to determine whether a significant difference in secondary transmission exists between these groups.

Journal

Open Forum Infectious Diseases – Oxford University Press

Published: May 22, 2023

Keywords: COVID-19; COVID-19 testing; SARS-CoV-2; public health; vaccination

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