COVID-19, updated guidelines from U.S. Centers for Disease Control and Prevention say.The guidelines — made public on Monday — said that a fourth dose could be administered with any vaccine that had been approved for use, including Janssen’s one-shot dose and mixed-dose regimens.“After completion of an mRNA primary series and an additional mRNA vaccine dose, moderately and severely immunocompromised people are eligible for a booster dose,” the updated guidelines read.Anyone eligible for the booster should wait at least six months between their third and fourth shot, the CDC added.Health Canada has not authorized booster shots with any vaccine, although the National Advisory Committee on Immunization (NACI) has recommended that seniors and.