I used to volunteer for a first aid organisation and often we would be providing support for large events like county shows or sports events.

The radios we used were simple VHF radios on licensed frequencies. There was no encryption which meant anyone could listen in, so obviously we weren't allowed to discuss personal details over the radio. Depending on the actual event we may be covering a large area or uneven terrain, so the radios may not always work.

For backhaul we'd either use our phone if we needed to call the emergency services or for larger events we'd have them onsite so they would forward the message on - for example to warn a hospital of an incoming patient (often it was in remote areas where the nearest hospital had limited A&E facilities) or to call an air ambulance.

Huawei's got a portable LTE Network that happens to be just for things like this. They call the technology eLTE (enterprise LTE) and the portable solution rapid eLTE. For backhaul you can use Fiber, Radio, Ethernet or Satellite, pretty much anything. the solution supports sending multimedia over the handys, voice, video, gps and data. They also offer a trunking solution over eLTE.

Satellite or long haul radio. Or they'll find one of the few remaining working trunk lines and serve it from there.