People who are #vaccinated against Covid-19 are less likely to #spread the #virus even if they become infected, a new study finds, adding to a #growing body of evidence that vaccines can reduce #transmission of the #delta #variant. British scientists at the University of Oxford examined national records of nearly 150,000 contacts that were traced from roughly 100,000 initial cases. The samples included people who were fully or partially vaccinated with either the Pfizer-BioNTech or the AstraZeneca vaccines, as well as people who were unvaccinated. The researchers then looked at how the vaccines affected the spread of the virus if a person had a breakthrough infection with either the alpha variant or the highly contagious delta variant. Both vaccines reduced transmission, although they were more effective against the alpha variant compared to the delta variant. When infected with the delta variant, a given contact was 65 percent less likely to test positive if the person from whom the exposure occurred was fully vaccinated with two doses of the Pfizer vaccine. With AstraZeneca, a given contact was 36 percent less likely to test positive if the person from whom the exposure occurred was fully vaccinated. The risk of transmission from a breakthrough infection was much higher if someone had received just dose of either vaccine. The study was posted online Thursday and hasn’t yet been peer reviewed. But scientists not associated with the research said the findings were credible. “It’s the highest quality study we have so far on the question of infectiousness of vaccinated people infected with delta,” said Dr. Aaron Richterman, an infectious disease physician at the University of Pennsylvania, who was not involved in the research. Susan Butler-Wu, a clinical microbiologist at the University of Southern California, called the study “well performed,” especially because it reflects real-world transmission since it tracked spread among close contacts. Using cycle threshold (Ct) values, the researchers found a similar level of viral load in unvaccinated and vaccinated people who were infected with the delta variant, backing up prior studies. Even so, people who were fully vaccinated were still less likely to infect others. “Transmission is much more complex,” Butler-Wu said, meaning the Ct value is just a snapshot in time and doesn’t reflect the entire course of illness. #NoiseCash