What Is A Cold Chain? And Why Do So Many Vaccines Need It?

Vaccines are like milk. Both make us stronger, but if stored at the wrong temperature, they spoil.

The reason? At least in the context of COVID-19, shots rely on messenger RNAs — particles, which in oversimplified terms, carry the key instructions for teaching your immune system to fight the coronavirus. mRNAs are fickle things, or as chemists would describe them, they're "unstable." They break down quickly unless adequately protected from those pesky enzymes which eat away at them.

Enter cold storage.

As countries race — and struggle — to deliver mass inoculations in far-reaching corners of the globe, the most formidable challenge for political leaders and public health authorities face is this: how do you transport tiny vaccine vials thousands of miles, keeping them at temperatures colder than an Arctic winter?

Of the three vaccines approved for rollout in many countries, the Pfizer vaccine wins for most high maintenance with storage requirements at -70 degrees Celsius (-94 degree Fahrenheit) — a bit chillier than record low temps at the South Pole. Pfizer announced Friday, however, that the vaccine can actually be kept at around typical home freezer temperatures (a balmy -25 to -15 degrees Celsius or -13 to 5 degrees Fahrenheit) for up to two weeks.