The Centers for Disease Control and Prevention has said people who are severely vulnerable or immunocompromised — including solid organ transplant patients, people with advanced HIV and certain cancer patients — should try to get a booster shot as soon as they can. But for people without severe immunocompromising conditions, getting a third dose soon after a second might actually be counterproductive, according to some public health experts. In an interview with MSNBC’s Andrea Mitchell this week, Dr. Anthony Fauci said people would be wise to give their immune systems a chance to “mature” before rushing to get a booster....