A new study from the University of California and the Chan Zuckerberg Biohub found “no significant difference” in viral load between vaccinated and unvaccinated people who were infected with the Delta variant of COVID-19. The study also found no significant difference in viral loads between symptomatic and asymptomatic people infected with the Delta variant of COVID-19.
The study, which is currently available as a preprint on MedRxiv, used cycle threshold values (Ct-values) to measure viral loads. A low Ct-value is indicative of a high viral load.
According to the study, “mean viral loads as measured by Ct-value were similar for large numbers of asymptomatic and symptomatic individuals infected with SARS-Cov-2 during the Delta surge, regardless of vaccine status, age, or gender. … We found no significant difference in cycle threshold values between vaccinated and unvaccinated, asymptomatic and symptomatic groups infected with SARS-CoV-2 Delta.”
The findings are consistent with the results of other recent studies analyzing the viral loads of vaccinated and unvaccinated people infected with COVID-19.
In a small Wisconsin study from earlier this year, Ct values were similar among vaccinated and unvaccinated individuals with COVID-19. Studies from both Massachusetts and Singapore likewise found similar Ct-values among vaccinated and unvaccinated individuals infected with the Delta variant.
The authors of the University of California study state that their findings “strongly support the notion” that vaccine status should not “influence the recommendation and implementation of good public health practices, including mask wearing, testing, social distancing, and other measures designed to mitigate the spread of SARS-CoV-2.”
The data comes as President Biden has ordered the Department of Labor’s Occupational Safety and Health Administration (OSHA) to issue a vaccine mandate for businesses with 100 or more employees.