Abstract
Objectives: SARS-CoV-2 viral load could be an important parameter for transmission potential. Here, we use quantitative reverse transcription-polymerase chain reaction cycle threshold (Ct) values as a proxy for viral load. We assess the effect of COVID-19 vaccination and prior infection status on Ct value while accounting for the virus variant. Methods: Using Dutch SARS-CoV-2 community testing data (n = 409,925 samples) from 8 March 2021 to 31 December 2022, separate univariable linear regressions were conducted for each explanatory variable, including age, sex, testing date, variant of infection, time since symptom onset, and testing laboratory. Subsequently, causal inference analysis assessed the impact of prior infection and vaccination status on Ct values, employing inverse propensity score weighting to adjust for confounders. Results: Our findings revealed a negative correlation between age and Ct values. Additionally, we observed modest differences in Ct values between different variants of infection, with lower Ct values (indicative of higher viral load) noted for Omicron variants compared to earlier variants. In addition, our results indicated an increase in Ct value (lower viral load) with prior infection. Conversely, the impact of vaccination was less pronounced. Conclusions: We observed an association between prior infection status and higher Ct values, suggesting a decrease in viral load, which could possibly indicate lower transmissibility.
| Original language | English |
|---|---|
| Article number | 107362 |
| Number of pages | 7 |
| Journal | International Journal of Infectious Diseases |
| Volume | 153 |
| DOIs | |
| Publication status | Published - Apr 2025 |
Bibliographical note
Publisher Copyright:© 2024 The Author(s)
Funding
This work was funded by the Ministry of Health, Welfare, and Sports (VWS). The Centre for Clinical Expertise at the National Institute for Public Health and the Environment (RIVM) assessed the research proposal following the specific conditions as stated in the law for medical research involving human subjects. The work described was exempted from further approval by the ethical research committee. Pathogen surveillance is a legal task of the RIVM and is carried out under the responsibility of the Dutch Minister of Health, Welfare, and Sports. The Public Health Act (Wet Publieke Gezondheid) provides that RIVM may receive pseudonymized data for this task without informed consent. The authors would like to thank all personnel at the 25 Public Health Services for data collection in the national surveillance database, the members of the RIVM genomic surveillance team, and the members of the RIVM COVID-19 surveillance and epidemiology team. Study design by SPA, MK, DE; Data collection by SPA, NvM, BV, MK, DE; Laboratory analyses by NvM, BV, SB. Data analysis and interpretation by SPA, JvdK, XW, HV, LP, JC, MK, DE; Writing by SPA, MK, DE. JC, MK, and DE were responsible for resources, supervision, project administration, and funding acquisition. All authors reviewed and approved the final version of the manuscript. Code for data processing, statistical analysis, figures, and tables can be found at GitHub (https://github.com/Stijn-A/SARS-CoV-2_Ct_value).
| Funders | Funder number |
|---|---|
| Ministerie van Volksgezondheid, Welzijn en Sport | |
| Speech Pathology Australia | |
| Rijksinstituut voor Volksgezondheid en Milieu | |
| National Institute for Public Health and the Environment |
Keywords
- Ct values
- Molecular epidemiology
- Prior infection
- SARS-CoV-2
- Vaccination
- Viral load