Vaccines, like many other things in the world, sometimes have a negative side attached to their main positive effect of protecting us against different – and potentially lethal – diseases.

Image credit: Tim Reckmann via Wikimedia (CC BY 2.0)

Luckily, this 'negative side' has a very, very low chance of manifesting in practice. Many different tests and clinical trials are being conducted to ensure the safety of vaccines. Therefore, the risk of using them is considered to be very low: every developer must provide compelling evidence proving this fact.

But still, the risk exists. So how high it is, and where is the acceptable risk level? The following video nicely explains the main principles behind the action of different vaccines, and also discusses the safety, possible side effects, and, of course, the bright side of their use, which is extremely important to every of us: