Alaina Yee, writing for PC World, about making a digital backup of your CDC vax card:

You should have a digital copy as backup. And make it a good one: It should be clear, sharp, and easy to read. You may need it as proof of vaccination or as a way to recall appointment details when trying to replace a lost card. And because your vaccination card displays sensitive personal information that can be used for identity theft, a digital version should also be kept secure.

Just did this:

• Scanned using Readdle’s excellent Scanner Pro
• Saved to iCloud
• Dragged into DEVONThink

How to protect your COVID vaccination card digitally: Dos and don’ts