After your dog's vaccination: normal reactions, red flags and the myths

Quick answer

A vaccine works by presenting the immune system with something to react to, so a mild reaction is the process working rather than a side effect. A dog that is quieter than usual for a day, sore where the needle went in, and slightly off its food is behaving normally.

The reactions that matter are separated from that by timing and by kind. Anaphylaxis arrives within minutes to hours and involves the face, the gut or the circulation. A lump that persists for weeks, grows, or becomes painful is a different problem again.

The useful window is the first few hours. Plan to be at home and paying attention rather than out for the afternoon.

• Mild lethargy and soreness for a day or two is expected and needs nothing.
• Facial swelling, hives, vomiting, collapse or pale gums within hours is an emergency.
• A small firm lump at the injection site is common. One that is still there weeks later needs checking.
• Vaccine dose is not scaled by body weight, which is why small dogs are not given less.
• Injection site tumours are a cat problem. They are not a recognised concern in dogs.

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Facial swelling, hives, vomiting, diarrhoea, collapse, pale gums or difficulty breathing after a vaccination is anaphylaxis and needs immediate veterinary attention.

It usually begins within minutes to a few hours, which is why it is worth staying nearby rather than driving straight to work. Puffiness around the muzzle and eyes is often the first sign, and it can progress quickly. Do not wait to see whether it settles, and do not give human antihistamines on your own judgement, because the doses differ and several human preparations contain decongestants that are dangerous to dogs.
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Decide in 60 seconds

What a normal response looks like and why

A vaccine contains either a modified live organism or killed material plus an adjuvant that stimulates the immune system. The body responds by recruiting immune cells to the injection site and mounting a systemic response. That response is inflammation, and inflammation is what produces the tiredness, the mild temperature rise and the soreness.

Expect a dog that sleeps more, is less interested in a walk, and may skip one meal. Expect a tender area under the skin. Expect normal drinking, normal toileting and a dog that responds to you as usual.

This should be resolving by the second day and gone by the third. A dog that is progressively worse rather than better on day two is not following the normal pattern.

Puppies often show it more than adults because they are receiving several components at once and because they are already busy with everything else in their environment.

Write down the date, which vaccine, which limb, and the batch number from the record card. If anything happens later, that is the information the vet needs.

The reactions that need attention, in order of speed

Anaphylaxis, within minutes to hours.

The immune system reacts violently rather than usefully. In dogs it commonly presents with facial swelling, hives across the body, sudden vomiting and diarrhoea, weakness and pale gums. Dogs differ from people in that the gut and the liver are often involved early, so vomiting can be the first sign rather than breathing difficulty.

This is treatable and treated quickly it usually resolves completely. It is an emergency because untreated it does not.

Injection site reaction, days.

A firm, sometimes slightly warm swelling under the skin where the vaccine went in. Most settle over a few weeks. What matters is whether it is still there after that, whether it is growing, whether it becomes painful, and whether the skin over it breaks down.

Lameness in the vaccinated limb, days.

Soreness in the leg for a day or two is ordinary. Persistent lameness is not, and it needs examining.

Immune mediated disease, days to weeks.

Rare, and worth knowing about rather than worrying about. The immune system turns on the dog's own red cells or platelets, producing pale gums, weakness, jaundice, bruising or pinpoint red spots on the gums and belly. Any of these need same day assessment whether or not a vaccine was recently given.

Behavioural change.

A dog that is subdued for a day is normal. A dog that is aggressive, disoriented, or having seizures needs a vet.

The myths worth correcting

"Small dogs should have a half dose."

They should not, and giving one risks a dog that is not protected. A vaccine dose is a quantity of antigen needed to trigger an immune response, not a drug dose calculated from body weight. Splitting it can mean the immune system never sees enough to respond to. If your dog has reacted before, the answer is a discussion about which components are needed and possibly pre-treatment, not a reduced volume.

"Vaccines gave my dog autism."

There is no such condition in dogs, and the human study that started this claim was found to be fraudulent and was withdrawn. Behaviour change in a young dog around the time of vaccination is far more likely to be adolescence, a fear period, or an unrelated illness.

"Vaccination causes cancer at the injection site."

This is a genuine and well recognised concern in cats, where injection site sarcoma has changed how and where cats are injected. It is not a recognised problem in dogs. A lump in a dog still needs checking if it persists, but the reason is different.

"Everything needs doing every year."

Modern core vaccines against distemper, adenovirus and parvovirus generally provide protection for several years after the initial course, and in many countries are given at longer intervals. Leptospirosis and kennel cough protection is shorter lived and is usually annual. Rabies intervals are set by law and by the product licence, and vary by country. The right schedule is the one your vet builds from the licences that apply where you live and from what your dog actually does.

"My dog never goes anywhere, so it does not need vaccinating."

Parvovirus survives in the environment for a long time and travels on shoes. Leptospirosis is carried by rodents and passes through water and soil. Neither requires your dog to meet another dog.

"Titres mean we never need to vaccinate again."

Antibody titre testing is useful and increasingly available for the core viral diseases, and a good titre is reassuring. A low titre does not necessarily mean an unprotected dog, because immune memory is not fully captured by circulating antibody. Titres do not work for leptospirosis or kennel cough. Treat titre testing as a useful tool in a conversation, not a replacement for one.

"You cannot vaccinate an old dog."

Age alone is not a contraindication. Illness on the day is. Older dogs may need fewer components rather than none, and a dog with a history of immune mediated disease needs an individual plan.

The first forty eight hours at home

Plan to be at home for the first few hours. This is the single most useful thing you can do, because the reactions with the shortest fuse are also the most treatable.

Keep the day quiet. No long walks, no swimming, no rough play, no training session that will exhaust a dog that is already tired.

Offer food normally. Do not force it and do not tempt with something rich, which just adds a stomach upset to the picture.

Leave the injection site alone. No massaging, no hot or cold packs, no ointment.

Bright eyes, normal gum colour and a dog that responds to you as usual are the reassurance. Pale or muddy gums are not.

Check the gums. Healthy gum colour is a reliable, quick indicator, and it is worth knowing what your own dog's gums look like when it is well.

Write it down: the date, which vaccine or vaccines, which limb, and the batch number from the record card. If a lump appears in three weeks, this record turns a guess into a fact.

Do not give any medication unless your vet has told you to. That includes human painkillers, several of which are seriously toxic to dogs, and human antihistamines, which are sometimes appropriate and sometimes contain other ingredients that are not.

Planning better vaccinations

Tell the vet about any previous reaction before the appointment rather than at it. A dog with a history can often be given components separately on different days, pre-treated, or kept in the practice for observation.

Do not vaccinate a dog that is unwell, has a temperature, has just finished a course of steroids, or is due for surgery in the next few days, without discussing it.

Time the appointment so it is not immediately before boarding, travel, a competition or a house move. Both because the dog needs a quiet day and because protection takes time to develop.

Ask which components your dog actually needs. Lifestyle vaccines depend on where you live, whether the dog swims, whether it boards, whether it goes to daycare, and what circulates locally. A sensible plan looks different for a farm dog and a flat-dwelling toy breed.

Keep the record card and photograph it. Boarding kennels, groomers and new vets all ask for it.

What never to do

Do not leave the dog alone for a long day immediately after vaccinating.

Do not give paracetamol, ibuprofen or any human painkiller.

Do not ask for or accept a reduced dose for a small dog.

Do not vaccinate a dog that is unwell without discussing it first.

Do not massage, heat, or apply anything to the injection site.

Do not assume a persistent lump is nothing because vaccine lumps are common.

Do not skip core vaccines for an indoor dog on the basis that it meets no other dogs.

Do not let a reaction go unrecorded. The next vet needs to know.

When to get help

Go immediately for facial or muzzle swelling, hives, sudden vomiting or diarrhoea, weakness, collapse, pale gums or any difficulty breathing after a vaccination.

Go the same day for a dog that is progressively worse on the second day, for pale gums or bruising several days later, for jaundice, or for a dog that will not get up.

The expected picture on day three is a dog that is entirely back to itself.

Book an appointment for a lump that persists beyond several weeks or is growing, for lameness in the vaccinated limb that has not settled, and before the next vaccination for any dog that has reacted before.

Bring the vaccination record card with the date, product and batch number, the time the signs started relative to the injection, photographs of any swelling with something for scale, and a note of any medication the dog was on at the time. That timeline is what tells the vet whether they are looking at a vaccine reaction or a coincidence.