The FDA has authorized a second dose of the updated Covid booster for older adults and people with weakened immune systems, which is designed to protect against the BA.4 and BA.5 variants of Omicron. This new bivalent formula will replace the multi-dose primary series for those who have not yet been vaccinated, and can be administered as early as four months after the first shot. It is hoped that this will help to reduce the spread of the virus and protect those who are most vulnerable.