Why is my cat still sick and lethargic 3 weeks after his vaccine?

Poor Izzie! It is doubtful that she is still having the side effects of the vaccines this far from when they were given. I am concerned that something else is going on and that this is a huge coincidence. I would talk to your vet to see what type of bloodwork they ran and if it would show why she may be acting this way. Since she got a little better but now feeling awful, I would consider having your vet do another exam. They will be able to run additional blood work, do a urinalysis or even do X-rays if needed. Also, they will be able to assess her hydration to ensure she isn’t dehydrated. There are so many different things that can cause lethargy, decreased appetite, and vomiting, but your vet will be able to narrow down the possibilities and get her started on some meds to help her feel better. I hope this helps!

Poor Jasper! The timing of his signs certainly correlate with his vaccine. Not eating and lethargy (as well as vomiting, diarrhea, facial swelling and hives) can be signs of a vaccine reaction. Vaccine reactions are uncommon, but do happen. If Jasper still isn't eating by later today, I would give your vet a call to have him rechecked. Some vaccine reactions require steroids and/or antihistamines for treatment.

This sounds like a side effect of the vaccine, it's not super common but i'v seen a few cases already and this usually resolves within 48-72 hours. your vet could give her pain killers for a couple days if her condition seems to be really bad.

No, this isn't normal behavior. While you can see a decrease in appetite and some lethargy, it's an unusual reaction to have a cat refusing to eat and drink, as well as not want to move. I would try to tempt her to eat by offering her some boiled white meat chicken (no bones) or soaking her food in tuna juice. If she still refuses to eat, then I would have her seen by a vet.

It is possible that Smokey is experiencing a vaccine reaction they can have a fever and be lethargic for 24 hours after the injections. If it persist longer than that I would return to the vet for medication. Be sure to notify your vet of this reaction so they can premed or split up the injections in the future

I think your vet's response was the correct one. All antibiotics carry a risk of intestinal upset and vaccines can certainly make pets feel "off". If he's not feeling better tomorrow, he needs to go back in to the vet.

I would take Mau Mau to he vet asap as it sounds like he is very poorly. He could have a nasty infection going on or could be feeling lousy from the vaccine. He may need supportive care until he feels well enough to eat again.