Vaccination Against SARS-CoV-2 Is Associated With a Lower Viral Load and Likelihood of Systemic Symptoms

Carolyn T. Bramante*, Jennifer L. Proper, David R. Boulware, Amy B. Karger, Thomas Murray, Via Rao, Aubrey Hagen, Christopher J. Tignanelli, Michael Puskarich, Ken Cohen, David M. Liebovitz, Nichole R. Klatt, Courtney Broedlow, Katrina M. Hartman, Jacinda Nicklas, Sherehan Ibrahim, Adnin Zaman, Hanna Saveraid, Hrishikesh Belani, Nicholas IngrahamGrace Christensen, Lianne Siegel, Nancy E. Sherwood, Regina Fricton, Sam Lee, David J. Odde, John B. Buse, Jared D. Huling

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Background: Data conflict on whether vaccination decreases severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load. The objective of this analysis was to compare baseline viral load and symptoms between vaccinated and unvaccinated adults enrolled in a randomized trial of outpatient coronavirus disease 2019 (COVID-19) treatment. Methods: Baseline data from the first 433 sequential participants enrolling into the COVID-OUT trial were analyzed. Adults aged 30-85 with a body mass index (BMI) ≥25 kg/m2 were eligible within 3 days of a positive SARS-CoV-2 test and <7 days of symptoms. Log10 polymerase chain reaction viral loads were normalized to human RNase P by vaccination status, by time from vaccination, and by symptoms. Results: Two hundred seventy-four participants with known vaccination status contributed optional nasal swabs for viral load measurement: median age, 46 years; median (interquartile range) BMI 31.2 (27.4-36.4) kg/m2. Overall, 159 (58%) were women, and 217 (80%) were White. The mean relative log10 viral load for those vaccinated <6 months from the date of enrollment was 0.11 (95% CI, -0.48 to 0.71), which was significantly lower than the unvaccinated group (P = .01). Those vaccinated ≥6 months before enrollment did not differ from the unvaccinated with respect to viral load (mean, 0.99; 95% CI, -0.41 to 2.40; P = .85). The vaccinated group had fewer moderate/severe symptoms of subjective fever, chills, myalgias, nausea, and diarrhea (all P < .05). Conclusions: These data suggest that vaccination within 6 months of infection is associated with a lower viral load, and vaccination was associated with a lower likelihood of having systemic symptoms.

Original languageEnglish (US)
Article numberofac066
JournalOpen Forum Infectious Diseases
Issue number5
StatePublished - May 1 2022


  • SARS-CoV-2
  • symptoms
  • vaccines
  • viral load

ASJC Scopus subject areas

  • Infectious Diseases
  • Oncology


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