Boosters are usually administered by injecting people with a second dose of the original vaccine. They are necessary because, over time, levels of circulating antibodies (an immunological proteins that can attach to pathogens and prevent them from infecting us) begin to drop, implying that protection goes off.
This second dose tells people's immune systems what the disease looks like, strengthening antibodies against it and preventing infection.
Depende po kasi sa vaccine iyan. Tsaka may tamang bilang naman ng booster shots every vaccine. Hindi naman porket may bagong variant, need kaagad may pa-booster shot. That's why may pagitan din na after 1, 2 or 3 months, kailangan nung second dose. To make your immune system become really familiar with the pathogen or virus.