The time it takes for a vaccine to become effective generally varies, but most vaccines begin to produce some immune response immediately, with full protection typically developing around 7 to 21 days after vaccination. For COVID-19 vaccines specifically, full immunity usually builds within about two weeks after vaccination, though people with prior infection or vaccination may develop immunity more quickly, often within 10 days. Protection from vaccines can wane over time, often starting to decrease after 3 to 6 months depending on the vaccine, variant, and individual factors. Booster shots are recommended to maintain or increase immunity. The exact timing for maximum effectiveness can differ by vaccine type and individual health status.