The effectiveness of COVID-19 vaccines typically decreases over time, particularly against infection and symptomatic disease, but remains relatively high against severe disease for several months after vaccination. Key points on vaccine effectiveness duration:
- Vaccine effectiveness against any SARS-CoV-2 infection and symptomatic COVID-19 disease tends to decline by about 20-30 percentage points within 6 months after full vaccination.
- Effectiveness against severe COVID-19 disease decreases more modestly, remaining above 70% for at least 6 months after full vaccination.
- The waning of vaccine effectiveness is partly due to declining immunity over time.
- In 2023-2024 data, vaccine effectiveness against medically attended COVID-19 was about 29-30% up to about 10 months, with more robust protection (48%) against critical illness, but this effectiveness waned over time after vaccination.
- The strongest protection occurs within the first 2 months after vaccination, after which it gradually declines.
- Continued evaluation is important to determine the duration of protection beyond 6 months and to guide booster dose recommendations.
In summary, COVID-19 vaccines offer the strongest protection against infection and severe disease within the first 2-6 months post-vaccination, with sustained high protection against severe outcomes for at least 6 months, but protection against infection diminishes significantly over that time frame. Booster doses are recommended to maintain immunity over longer periods.
