Thumbnail Audit of Adverse Vaccination Events

If justifying your decision against vaccination in terms of feared side effects, it’s important to get your facts right.   Here we’ll look at the types of side effects dogs and cats may suffer after inoculations, and estimate the risks of each for pets in Australia, in 2008. Let’s put the case against vaccination into context.




Every year the APVMA, the federal government authority that regulates veterinary medicines, reports on adverse drug events. It tallies vaccination reactions, drug side effects and cases of pesticide toxicity.

I’d like to say it makes interesting reading but, to be honest, it’s rather dry. You can freely download it but to save you the time, wading through over 100 pages of lists, I’ve shrunk it down to more digestible proportions.

It’s also important to acknowledge the limitations of this data, and the methods used to condense, however the impatient or bored can jump straight to the risks and summary at the end.

Limitations of the Data

Compared with the extensive pharmacovigilence in man, veterinary medicines are only superficially monitored. Informing the APVMA of adverse events is voluntary and if an incident was mild, predictable and occurred in isolation, reporting can easily drop to the bottom of a vet’s crowded to-do list.  More serious incidents and cluster or ‘batch’ events would be more diligently reported, and numbers should be more accurate for such occurrences.

Delayed adverse effects  like auto-immune disease, occuring up to months later, are hard to pin-down as vaccine-induced and are probably  underreported. In contrast,  immediate adverse effects should be more easily spotted. Vaccinations are usually given to healthy animals so a ‘turn for the worse’ is easier to identify as side effect rather than any underlying disease.

That being said, there would be a significant number of mild vaccine reactions that pass, unrecognised by pet owners; others not reported by pet owner to vet; and many not reported by vet to regulatory authority.

The manner in which the APVMA collates and publishes this data, as a collective list of overlapping clinical signs and diagnoses with either ‘possible’ or ‘probable’ causality, makes numerical analysis difficult.  Adverse reactions to combination products, which includes most vaccinations, are hard to define as resultant form a single ingredient.

Adverse effects of vaccinations are not aggregated under a particular branded product, say Canvac 3, or Protech PI2. Instead they are grouped collectively under specific pathogens against which vaccines are designed to be protective (eg Parvo, Hepatitis, Herpes etc). Unfortunately, this deprives us of important information: a national consumer survey of which vaccines are safest. Vaccine manufacturers are unwilling to release such information as no one company is certain their product is the safest, and at least one of them would lose market share if  over-represented in the side effect statistics.




  1. Most vaccines are delivered as combination products and some aggregation of data helps to cut the processing load without losing the central message.
  2. Causative links between misadventure and vaccination are rarely concrete, especially if delayed by days or weeks, and events are described as possible or probable. The aggregation of these subsets may slightly overstate incidence.
  3. As many clinical signs would occur in the one patient, most figures overstate the incidence of side effects and attention should be paid to the total number of reports at the top of each column. The 132 C3 incidents would be a partial subset of the 140 Kennel Cough reactions, as they would be given together as a C5.
  4. Figures for diagnostic descriptors: autoimmune diseases, anaphylaxis and death, would not overstate incidence as significantly as clinical signs.  These deserve individual attention and are tallied separately.
  5. There are a range of local injection site, non-specific, gastrointestinal and cardiorespiratory signs, and those typical of angiooedema/urticaria, tallied collectively.  These may be milder events or signs associated with the more severe events described in 4. Their grouping is detailed as follows:
  • Severe systemic includes clinical signs of anaphylaxis, pulmonary oedema, loss of consciousness, and circulatory failure (hypotension, rhythm disturbance)
  • Autoimmune states include haemolytic anaemia, thrombocytopenia, polyarthopathy and epistaxis.
  • Local includes pain, swelling, abscesses, erythema, alopecia or lumps at the injection site.
  • Moderate systemic includes signs of angiooedema, urticaria, and pruritis.
  • Gastronintestinal includes vomiting, diarrhoea, salivation, and haemorrhagic gastroenteritis.
  • Respiratory includes, cough, sneeze, occuonasal discharges, or changes in breathing pattern.
  • Non-specific includes lethargy, malaise, agitation, restlessness, fever, urination, weakness, vocalisation, myalgia and anorexia.


What’s the Chance of an Adverse Vaccination Reaction?

Reading though these lists of medical terms you may feel your doubts about vaccination safety are vindicated. However, without accurate figures on the total number of animal vaccinations given each year, these numbers are a little meaningless.  We  can extrapolate from data abroad, however……



The percentage of cats in the United Kingdom receiving vaccination is estimated at 30%. Australia could be lower, but even if as low as 20% our feline pet population of about 2.4 million would receive almost half a million vaccines doses each year.

So the likelihood of a ‘bad’ vaccination experience for cats, sufficiently serious to be reported to APVMA, is about 1 in 20,000. Within this group of cats:

  • The chance of a more severe,  but non-fatal reaction about 1 in 100,000;
  • The chance of vaccine-induced death is about 1 in 250,000.
  • Anaphylactoid reactions in cats are less frequent than in dogs, but more commonly fatal.

Before you start to believe that Chlamydia and Leukaemia are better vaccinations with less adverse events, you need to consider they’re given far less frequently than the F3. Ironically, vaccination against Chlamydia is one I would avoid if looking to reduce the likelihood of an adverse event.



The Australian dog population is about 3.5 million but without an accurate figure on the number vaccinated each year, the numerical odds of a side effect are guesstimates only. Some general statements that can be teased out of the data, however:

There are about 140 adverse reactions to canine vaccinations; in about 15 of which, Kennel Cough vaccination was deemed the culprit.  If 30% of Australian dogs were vaccinated each year:

  • The risk of a local, injection site reaction is about 1 in 20,000;
  • A moderate allergic reaction is about 1 in 30,000;
  • A severe but non-fatal reaction 1 in 100,000;
  • And a serious autoimmune disease about 1 in 200,000.

If looking to avoid a local injection site reaction, requesting an intranasal Kennel Cough vaccination, delivered not by injection but dribbled into the nostril, will significantly cut your chance of an adverse event.



Adverse events aren’t only side effects of a product, but also their failure. Every year small numbers of animals catch a disease against which they’re vaccinated. Given many of these diseases have high mortality rates, vaccination failure can be as catastrophic as fatal anaphylaxis to an inoculation.

Such events shouldn’t be blamed on manufacturers as there are multiple potential weak points in delivery of vaccine from pharmaceutical vat to pet’s bloodstream. Failure to keep vaccines chilled to 2-8C during journey between manufacturer, distributors, and consulting room; insufficient or poorly timed boosters; or just an idiosyncratically poor immune response of the patient, are obvious potential causes of vaccination failure.

There is also the reality that, while researchers are constantly looking for vaccination recipes that result in more protective, long-lasting, and broad-spectrum immunity, viral and bacterial genomes are sufficiently diverse and dynamic that some strains may side-step the immune system of a vaccinated animal.

Failure rates are very low and commonly associated with unusual, non-core vaccines known to offer only partial immunity, or cover only particular strains. Leptospira inoculation is the most notorious.




Sure, these figures seem a bit rubbery but they’re all we’ve got.  There are aspects of this ‘analysis’ which both over- and understate the incidence of vaccination reactions, hopefully balancing things to some degree. Even when we acknowledge these limitations, the odds of a significant adverse vaccination event are very low. This doesn’t imply we should ignore these negative impacts altogether.

Most of us expect some degree of vaccination reaction when we recieve an inoculation ourselves, or seek such treatment for our pets. Yet all of us would be devestated to lose our pet to a fatal reaction to inoculation, or a preventable disease if we failed to vaccinate. So where’s the middle ground?

In an ideal world we should vaccinate only often enough to sustain a protective titre of antibody.  For those pet owner who can  afford this – Go for it! Vets are usually interested in the results of such inquiry. Many pet owners, however, would find it inhibitively expensive to conduct blood tests to monitor the need for vaccination, and would prefer to run the slight risk their pet suffers the consequences of over-vaccination.

Applying to vaccination the Goldy Locks principle of not too much, not too little, some things to consider are:

Vaccinate on time in  puppyhood. Incorrect timing may result in failure to induce protective immunity, which may require extra vaccinations to correct.

Ask about vaccination protocols that are longer acting and have less side effects.

If your pet suffers an adverse reaction to vaccination, the severity will influence decision-making surrounding further vaccinations. If mild and local, many vets will be undeterred. If serious and systemic, repeat vaccination may be more dangerous than the risk of disease. Serology titres may be useful for determining frequency of boosters in such cases.

.Look at your levels of  disease risk in adulthood:

  • If your cat never leaves the 10th storey apartment, you may choose to vaccinate less frequently or  not at all.
  • Dogs who hang out with many others at the beach or park, or share territory with foxes, should keep C3 up to date, at least.
  • In short-faced dogs who can barely breathe when healthy, Kennel Cough vaccination may also be life-saving.
  • Cats who socialise/fight with others have a much higher risk of diseases we vaccinate against, and adding FIV may be of merit.



  • Child Vs Tool on the varying levels of emotional engagement between pet and owner.

Tags: , , , , , , , , , , , , , , , , , , , , , , , ,

2 Responses to “Thumbnail Audit of Adverse Vaccination Events”

  1. Jill Maddison says:

    Well done Matt. Excellent balaned report. Proud of you (-:

  2. We agree, a well researched, balanced article

Leave a Reply