Viral dynamics of the SARS-CoV-2 Omicron Variant among household contacts with 2 or 3 COVID-19 vaccine doses.

Objectives: SARS-CoV-2 shedding has changed as new variants have emerged. It is important to understand the trajectory of PCR positivity due to Omicron in vaccinated populations.

Methods: Double- or triple-vaccinated adult household contacts of individuals with COVID-19 self-collected oral-nasal swabs for 14 days. A hierarchical linear model estimated viral load trajectories and an exploratory logistic regression model assessed for factors associated with viral detection before symptom onset.

Results: Forty-one participants developed COVID-19 with 37 (90%) symptomatic. Viral load peaked 3 days after symptom onset at a median concentration of 8.83 log copies/milliliter (range 5.95-10.32) and the mean difference between participants with two or three COVID-19 vaccine doses was 0.02 log copies/milliliter (95% CI -0.13 to 0.16). PCR positivity began with a range of 4 days prior to 3 days after symptom onset and was positive on the day of symptom onset in 76% (28/37). SARS-CoV-2 detection on the day of symptom onset was less likely among those with 2 vaccine doses (OR 0.13, 95%CI 0.02-0.79). 68% (25/37) of infected participants had detectable SARS-CoV-2 with Ct<30 at 7 days after symptom onset.

Conclusions: Peak viral load and duration of PCR positivity were similar in participants with COVID-19 after two versus three COVID-19 vaccine doses. Onset of viral detection relative to symptom onset was variable.