The relationship between COVID-19 viral load and disease severity: A systematic review

Immun Inflamm Dis. 2022 Mar;10(3):e580. doi: 10.1002/iid3.580. Epub 2021 Dec 13.


Introduction: Patients with COVID-19 may present different viral loads levels. However, the relationship between viral load and disease severity in COVID-19 is still unknown. Therefore, this study aimed to systematically review the association between SARS-CoV-2 viral load and COVID-19 severity.

Methods: The relevant studies using the keywords of "COVID-19" and "viral load" were searched in the databases of PubMed, Scopus, Google Scholar, and Web of Science. A two-step title/abstract screening process was carried out and the eligible studies were included in the study.

Results: Thirty-four studies were included from the initial 1015 records. The vast majority of studies have utilized real-time reverse transcription-polymerase chain reaction of the nasopharyngeal/respiratory swabs to report viral load. Viral loads were commonly reported either as cycle threshold (Ct ) or log10 RNA copies/ml.

Conclusion: The results were inconclusive about the relationship between COVID-19 severity and viral load, as a similar number of studies either approved or opposed this hypothesis. However, the studies denote the direct relationship between older age and higher SARS-CoV-2 viral load, which is a known risk factor for COVID-19 mortality. The higher viral load in older patients may serve as a mechanism for any possible relationships between COVID-19 viral load and disease severity. There was a positive correlation between SARS-CoV-2 viral load and its transmissibility. Nonetheless, further studies are recommended to precisely characterize this matter.

Keywords: COVID-19; SARS-CoV-2; prognosis; severity; viral load.

Publication types

  • Review
  • Systematic Review

MeSH terms

  • Aged
  • COVID-19*
  • Humans
  • SARS-CoV-2*
  • Serologic Tests
  • Severity of Illness Index
  • Viral Load / methods