People who are unvaccinated spread the COVID-19 delta variant virtually the same as the vaccinated, according to a study in a federal prison funded by the Centers for Disease Control and Prevention.
“In this investigation, we found no statistically significant difference in transmission potential between vaccinated persons and persons who were not fully vaccinated,” the researchers said.
“Therefore, our findings indicate that prevention and mitigation measures should be applied without regard to vaccination status for persons in high-risk settings or those with significant exposures.”
The study, published on medRxiv, was a joint project of Cold Spring Harbor Laboratory, Yale University and the British Medical Journal.
The researches said their data “add to a growing body of evidence characterizing transmission potential from vaccinated persons.”
However, they acknowledged the small proportion of participants in the study who were not fully vaccinated, 17, “and negative findings reported here warrant cautious interpretation.” A total of 78 were fully vaccinated.
“To increase the sample size of this group, two partially vaccinated participants were included, potentially diluting the characteristics of unvaccinated participants,” they wrote. “However, our conclusions did not change when analyses were performed excluding these two participants.”
A long-term study in the U.K. published in October found the rate of transmission in households that were fully vaccinated was statistically the same as unvaccinated households.
In Israel, a fully vaccinated person was determined to be the source of a clinic outbreak in which 16 health-care workers, 23 patients and two family members were infected. Fourteen fully vaccinated patients became severely ill or died. There were two unvaccinated patients, and they developed only mild disease.
The Centers for Disease Control identifies four of the top five U.S. counties with the highest percentage of the population fully vaccinated (99.9–84.3%) as “high” transmission counties.
In Canada, the government’s chief health minister, Theresa Tam, confirmed that people who have been fully vaccinated have viral loads similar to the unvaccinated, meaning they can transmit the virus.
In October, researchers at the University of California, Davis, Genome Center, UC San Francisco and the Chan Zuckerberg Biohub released a study finding no significant difference in viral load between vaccinated and unvaccinated people who tested positive for the delta variant of SARS-CoV-2.
The study also found no significant difference between infected people with or without symptoms.