Zip code is a bit too granular. You should add a distance radius, or something broader like a county. I would gladly travel 50+ miles to get a vaccination.
Good point...thought about doing a typeahead for nearer zip codes if the zip code searched doesn't show up results. Counties are interesting idea, but the bucketing needs to be simplified to lat/lng for data ingestion, which is why zip codes were chosen, arguably the most intuitive thing that's "close enough" to a lat/lng coord.
Dunno what search backend you’re using, but if it’s ElasticSearch this can be done pretty quickly with a Gaussian decay filter. That takes in lat/lng directly, and adjusts the ordering of results.
That’d also give the nifty feature of finding the closest available vaccine, even if it’s a hundred miles away (not a walk in the park, but I’d drive that far personally)