The effectiveness of COVID-19 vaccines typically decreases over time. Studies show that vaccine effectiveness against infection and symptomatic disease decreases by about 20-30 percentage points within six months after full vaccination. However, the protection against severe disease remains higher and more durable, with most vaccines maintaining greater than 70% effectiveness against severe COVID-19 up to six months post-vaccination. Recent data from 2023-2024 vaccines also indicate that vaccine effectiveness wanes over time, with highest protection shortly after vaccination and reduced protection several months later. For example, vaccine effectiveness against COVID-19-associated hospitalization was about 51% in the first two months post-vaccination but declined significantly after six months. Booster doses are recommended to sustain and enhance immunity, especially against severe disease and new variants.
