Originally Posted by Missy May
If it were me, I would at least go purchase a 5-way and give it to her. Record it, keep the lot number and type "tab" from the shot for your records. Done. You know when your others were last immunized - I would remove all doubt for the new one. If it would give you peace of mind, call your vet and ask him if this is advisable (i.e., "what if" she had them 6 months ago, will it matter).
Buying shots from a feed store is sometimes a waste of money. If they weren't held at the right temperature throughout shipping, stocking, storage, etc. then they won't be effective. There have been quite a few studies showing that "over the counter" vaccines have been handled improperly and you might as well be injecting saline. I'd agree that there is no harm waiting a month or so and then doing everyone at once. You can bump your current horses up a month too, vaccines don't need to be given precisely on schedule, but try to keep within a month or two.