The CanSino researchers suggested the dampening of the immune response due to preexisting immunity to the Ad5 vector might be overridden by using a booster dose sometime between three and six months after the original dose — a potentially awkward dosing regimen that would not deliver rapid protection in the people who are at highest risk from Covid-19, older adults. Edwards said, though, that another dose might simply boost the immune response to the Ad5 vector, not the intended target, SARS-CoV-2.