Booster provides optimal protection. but the cdc says just two shots. so when will that change? jacqueline howard joins us now. jacqueline, what's the latest on? >> reporter: john, the latest on this is we could see the definition change. but when that will happen is what remains unclear. there are some logistic cal challenges with updating the definition. if you remember, about a year ago when vaccine makers got their vaccines authorized, they applied for emergency use authorization, noting that a preliminary series is just two doses. so in their authorization applications they said two doses...