how long after covid shot is it effective

Studies suggest that COVID-19 vaccines become effective about two weeks after receiving the shot, as it takes this time for the body to build up the protective immune response. The vaccines are most effective in the first few months following the shot, which is why booster doses are recommended approximately three to four months after the last dose to maintain protection. The immune response continues to strengthen in the weeks after vaccination, but vaccine effectiveness can wane over time, necessitating boosters especially with new variants circulating.