The COVID-19 vaccine booster starts working almost immediately after administration, but it typically takes around two weeks to reach maximum protection. The booster effectiveness is highest in the first month after the shot, with significant protection against infection and severe disease, although the protection against infection gradually wanes over months after the booster.
Key Points on Booster Effectiveness
- Immune response begins almost immediately after the booster.
- Maximum protection is usually reached about two weeks post-booster.
- Booster effectiveness against infection is highest (~61%) during the first month.
- Protection against severe COVID-19 is substantial (~75%) and lasts longer.
- Effectiveness against infection decreases over six months but still provides some benefit.
- Boosters are especially important for clinically vulnerable individuals to reduce severe disease risk.
This means one is best protected from COVID-19 approximately two weeks after receiving a booster dose, with the strongest protection in the first month and lasting substantial protection against severe illness for at least several months thereafter.
