"Vaccines are not, even as good as they are and highly effective, nothing is 100%." "If you put yourself in an environment in which you have a high level of viral dynamics and a very low level of vaccine, you might want to go the extra step and say 'When I'm in that area where there's a considerable degree of viral circulation, I might want to go the extra mile to be cautious enough to make sure that I get the extra added level of protection, even though the vaccines themselves are highly effective," he said.