Early results show that this vaccine, developed by CanSino Biologics, appears to be safe and generate an immune response. It uses an adenovirus (Ad5) that can easily enter human cells. Researchers across several labs tested the vaccine in a total of 108 patients, according to the study published in Participants were given a low, medium or high dose, as a single injection. They had a moderate immune response, peaking at day 28 after receiving the vaccine. The highest dose was more immunogenic than the other two. The most common complaint following injection was pain at the site, though nearly half of the subjects also had a fever, headache and fatigue. These were more common among people getting the highest dose of vaccine. About 20 percent had muscle pain as well. It is not known how long the antibody response prompted by this vaccine may last, and these results are not enough to prove that the vaccine can protect people from COVID-19 infection. Once concern about this vaccine is that many people have already been exposed to Ad5 adenovirus and may have antibodies to it, which could limit the effectiveness of using it as a mechanism for vaccine delivery.