A booster shot is a medical procedure in which a person receives an additional DOSE of a vaccine. The term 'booster shot' can also refer to any injection that provides a boost of energy or strength. In this crossword, the solutions HYPO, DOSE, and TURBO all relate to the term 'booster shot'. HYPO is a four letter word meaning 'under or below normal', which could refer to the amount of the vaccine given in a booster shot. DOSE is a four letter word meaning 'a measured quantity of medicine taken at any one time', which could refer to the amount of the vaccine given in a booster shot. TURBO is a five letter word meaning 'providing extra power or speed', which could refer to the effect of the booster shot on the body.