Originally Posted by JFS 3

The vaccine reduced viral load and symptoms for virtually all populations. This virus is airborne and is largely spread through symptoms - sneezing and coughing. Reducing symptoms and viral load thus reduced the spread of the virus.

This isn't up for debate or even hair-splitting - it's just the truth. A very simple one. There are a great many opinions about the vaccine itself and associated policy, but how the vaccine worked isn't a mystery at all.