WHO reports that protection against severe disease and death is highest in the first few months following vaccination and subsequently decreases.
This does not mean protection suddenly disappears.
It means the level of protection can gradually decline.
That is why vaccination recommendations can change as scientists collect additional evidence.
- The virus changes
SARS-CoV-2 has produced multiple variants over the course of the pandemic.
Some variants have been able to spread more efficiently or partially evade existing immunity.
The WHO notes that viruses can change over time and that emerging variants
