Here are the latest theories regarding the reasons for extreme thirst after a Covid-19 shot.
Developing a fever is a great contributor to dehydration as the water literally evaporates from the body quicker, and you lose salts and fluids.
Another possibility is that the enlarged toll on the immune system leads to thirst. Much of the water in our body is stored in the blood and vessels connected to it, such as lymph nodes. An immune reaction activates the tonsils, the adenoids, white blood cells and your lymph nodes, causing thirst to compensate for the excessive load on the immune system. The thirst isn't a sign that there's something wrong. It is on the contrary; it means your body is working well.
Other less common theories suggest that this may be simply because of stress, or because you were dehydrated before the shot and now the thirst feels more present as you're paying more attention than usual to your body after the shot.
Should you choose to receive the vaccine, it is recommended to enjoy a nutritious meal beforehand, come well-hydrated and avoid taking painkillers before the shot.
Lastly, it is important to remember that experts are still learning as we go, and that what we know today may not be the full picture yet, or may not even be valid tomorrow.