What's tiny, transformative, smart, and now 5 billion strong?

Imagine you are a health care worker. Should you use or discard the vaccine at right?

For years, health care workers had no way to decide. Then, nearly two decades ago, PATH and our partners developed and introduced the tiny, powerful vaccine vial monitor (VVM).

VVMs change color as they are exposed to heat, letting providers know at a glance whether heat-sensitive vaccines have been damaged or can still be used for immunisation.

As of 2014, 5bn VVMs have been used, saving lives by ensuring vaccines are still potent when they are given.

Thanks to vaccine vial monitors, health care workers, like this one preparing to vaccinate a young girl in Laos against Japanese encephalitis, can quickly see if the vaccine has been exposed to excessive heat. Photograph: Aaron Joel Santos/PATH

Five billion is an enormous number. That many VVMs, end to end, would circle the globe. It's more than two VVMs for every one of the 2 billion children on earth.

And our impact continues to grow. In the next decade, we estimate that VVMs will allow health care workers to recognise and replace more than 200m damaged doses and deliver at least a billion more doses in remote settings.

Thanks to the vision and tenacity of Path and our partners, we did what no other group could: unlock a simple, transformative innovation and drive it to lifesaving scale.

Exemplifying our role in leading global health innovation, Path was selected as one of 30 leading American innovators for the US Global Leadership Coalitions's (USGLC) 2014 Innovations in Smart Power Initiative, in which the VVM was selected as a top life saving innovation.

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