Scientists at Imperial College London say they are immunizing hundreds of people with an experimental coronavirus vaccine in an early trial after seeing no worrying safety problems in a small number vaccinated so far.

Dr Robin Shattock, a professor at the college, told The Associated Press that he and colleagues had just finished a very slow and arduous process of testing the vaccine at a low dose in the initial participants and would now expand the trial to about 300 people, including some over age 75.

"Well tolerated. There are not any side effects," he said, adding it was still very early in the study. Shattock, who is leading the vaccine research at Imperial, said he hopes to have enough safety data to start inoculating several thousand people in October.

Since have dropped dramatically in Britain, making it difficult to determine whether or not the vaccine works, Shattock said he and his colleagues are also looking to test their vaccine elsewhere.

"We are looking very carefully at the pandemic, at the numbers where the hot spots are and talking to collaborators that have the facilities to do these kinds of studies," he said.