TORONTO – One dose of one vaccine, one of another: when in the absence of available alternatives at the time of recall, injections of different vaccines were offered, many people accepted. After all, the scientific community tried to reassure everyone, the benefits would have been the same. Then, slowly, the effectiveness of a mixed vaccination regimen was questioned. Or at least doubts have arisen for lack of an experimental basis on which to base the decision. And many countries in the world have decided not to authorize, for example, vaccines such as AstraZeneca, called into question for the risk of developing thrombotic events such as heart attacks and pulmonary embolisms. →