Only smart syringes that break after one use should be used for injections by 2020, the World Health Organization has announced.

Reusing syringes leads to more than two million people being infected with diseases each year, including HIV and hepatitis.

The smart ones prevent the plunger from being pulled back after an injection, so they cannot be used again.

The new needles are more expensive, but the WHO says the switch would be cheaper than treating the diseases.

But how does this smart syringe work?