By October 24, 2019 February 12th, 2020 Preventative Medicine

Recent advances in veterinary medical science have resulted in an increase in the number and type of vaccines that are available for use, and improvements are continuously being made in safety and efficacy. Some vaccines are routinely advocated for all pets (‘core’ vaccines) whereas others are used more selectively according to circumstances. However, in all cases, the selection of the correct vaccination program for each individual pet, including the frequency of repeat, booster, vaccinations, requires professional advice.

How do vaccines work?

Vaccines work by stimulating the body’s defense mechanisms (the immune system) to a particular microorganism or microorganisms (virus, bacteria, or other). The animal’s immune system is then prepared to react to a future infection with that microorganism(s) and either prevent infection or respond and eliminate the microorganism to give rapid recovery. Vaccination stimulates the immune system similarly to a natural infection with a particular infectious agent, but typically with far less illness than natural disease, and then provides protection for the future.

One of the most important components of the immune system are protein molecules called antibodies. A specific microorganism has components called antigens that induce the immune system to produce antibody that specifically binds and neutralizes that organism and no other. Antibodies work together with white blood cells (lymphocytes) that are able to identify and kill those cells that have become infected by the microorganism.

After vaccination, just as after recovery from natural infection, the body ‘remembers’ the particular antigens so that when they are encountered again it can mount a rapid and strong immune response thereby preventing your pet from developing the disease. It is important to realize that most vaccines work by preventing your pet from becoming ill during a subsequent exposure to specific disease-causing organisms, but vaccination may not prevent them from becoming infected. In such cases your pet, while itself protected against disease, may shed the organism for a period of time after exposure and be capable of infecting susceptible animals with which it is in contact.

Immunity is not absolute. Immunity can sometimes be overcome when there is an overwhelming exposure to a high dose of a virulent (particularly harmful) strain of the microorganism or when the animal is unduly stressed or its immune system is otherwise depressed (immuno-suppression) by other infections or certain drugs.

What is a modified-live vaccine?

In a modified-live or live-attenuated vaccine the causative organism (virus, bacterium, etc.) has been altered so that it is no longer harmful (‘virulent’) but upon injection or other administration it will stimulate protective immunity.

What is a killed vaccine?

The organism has been killed (‘inactivated’) to render it harmless. Killed vaccines often need a helper or ‘adjuvant’ included in the vaccine to stimulate a longer-lasting immune response.

Which is better: a live or killed vaccine?

Both have advantages and disadvantages. Your veterinarian takes many circumstances into account in making the choice.

What are the risks of vaccination?

There are very few risks to vaccination. Your veterinarian will be able to advise you on specific details concerning your pet. Occasionally you may notice your pet has a temporary loss of appetite or is less lively a day or two after a vaccination, but this should resolve within 24 to 48 hours. In a very few cases, they may be allergic to one or more components of the vaccine and have more serious side effects such as vomiting or diarrhea, or facial swelling which could lead to difficulty in breathing. If these signs occur, let your veterinarian know immediately. A rare form of soft tissue (cancer) has been associated with certain vaccine components in a very small number of cats. This was more common with older vaccines in the 1980’s and 1990’s.  Studies are still in progress on this, but the benefits of vaccination greatly outweigh these small risks for most situations.

Will vaccination make my pet sick?

It is not unusual to detect some lethargy in the day or so after vaccination. In the case of killed vaccines containing an adjuvant, some thickening or lump formation may occur at the vaccination site. If this is painful or persists for more than a week or so with no decrease in size, consult your veterinarian. A few dogs will develop more severe reactions that are forms of hypersensitivity (allergy). These will usually occur within minutes but may be delayed for a few hours. Your pet may have difficulty breathing, salivate, vomit, and have diarrhea. In these situations consult your veterinarian immediately.

Do vaccines provide 100% protection?

Vaccines have been highly successful in protecting the majority of pets against diseases that were once common but are now rare, but there are situations in which the immunity conferred by a vaccine may be overcome and a vaccinated pet may still develop disease. In such cases the disease is generally milder than it would have been had the animal not been vaccinated. Some causes for apparent ‘vaccine failure’ are:

  • Maternally derived antibodies. Newborn animals have not yet had a chance to make their own immunity so they need protection against infections present in their environment. They receive this immunity from their mother, partly across the placenta while in the uterus with most of the maternal antibody transferred to them in the first milk or colostrum. So a well-vaccinated female will confer antibodies to the diseases she has been vaccinated against and any others she has acquired naturally to her young. Such antibodies protect the newborn against those diseases for the first 2 or 3 months of its life (the most critical period). However during this same period the maternally derived antibodies can block the effects of vaccines. This blocking effect gradually disappears over those 2 to 3 months. At this point in time a vaccination can be successfully given.
  • Incomplete immune response. There is variation between pets in their immune system. Some respond less well to vaccination, so immunity may be incomplete or shorter-lived than normal. Certain breeds and genetic lines have a tendency for such problems.
  • Declining immunity. Without booster vaccinations, or without natural boosting of immunity by sporadic exposure to the infectious agent in nature, immunity to the specific organism declines over time, particularly in older age. There may come a time when if there is a particularly heavy dose of the organism from the environment the declining immunity may be insufficient and overwhelmed and result in disease.
  • Immune suppression. Certain infections and some drugs, such as anti-cancer drugs, may cause a suppression of the immune system so that an otherwise well-vaccinated pet becomes susceptible to infection and disease if exposed.
  • New strains of organism. Some infectious agents exist in different strains or new strains evolve, that are not directly covered by the vaccines given. There may be some ‘cross-protection’ but it may not be complete.

The above are not the only reasons for vaccination ‘failure’ but they are the most likely explanations.

When should my puppy or kitten be vaccinated?

The first vaccine should be given at 8 weeks of age, a second dose is given at 12 weeks and a third at 16 weeks of age. Your pet will not be fully protected until 7-10 days after the final vaccination. Under specific circumstances your veterinarian may advise an alternative regime.  Vaccines given prior to 8 weeks are generally ineffective, and the subsequent regime will be adjusted to accommodate for early vaccines.

How long does it take for a vaccine to produce immunity?

Within a few hours of vaccination the earliest phases of the immune response are being stimulated. It usually requires 10 to 14 days before a reasonable level of protection is established. Killed vaccines may not provide adequate protection until after the second dose. Also in young puppies maternal antibody may hinder protection until later in the vaccine series. Therefore it is advisable to keep a recently vaccinated puppies and kittens away from dogs or cats of unknown vaccination history until it has finished its vaccination course.

If you feel your pet has contracted an infection for which it has been vaccinated then let your veterinarian know so tests can be undertaken to try and establish why vaccination has failed to be protective.

Which vaccines are needed in cats?

Depending on your locality some infections may be more or less likely. Your veterinarian will assess the relative risks based on your circumstances and advise you accordingly.

Feline panleukopenia infection

This is an uncommon disease today because of widespread vaccination, but the risk remains widespread. When disease occurs it is a severe and often fatal gastroenteritis, with profound depression, dehydration and collapse. It is very contagious to other cats. Vaccination provides a high level of long lasting protection.

Feline respiratory virus infection

Disease is caused by FVR virus (FHV-1) or the caliciviruses (FCV) – sometimes together. The syndrome is commonly termed Upper Respiratory Infection (URI) or sometimes, erroneously, “Cat Flu”. While not usually very serious (except in young kittens) it is a very common infection in unvaccinated cats and can cause long-term problems. Vaccination is only moderately effective as solid immunity to these viruses is not long term, and may be overcome by a high dose of virus in the immediate environment. Vaccination does significantly reduce the severity and duration of URI. Cats at high risk may require twice yearly vaccination, at least initially, to provide better protection.

Feline chlamydial infection

This tends to be a particular problem in colony cats. Chlamydiosis is a bacterial infection causing a painful inflammation and swelling of the conjunctiva (the membrane around the eye) and has been associated with infertility in queens. Infection in colonies of cats can last for long periods because protection against re-infection (immunity) is relatively short lived. Vaccination can help to prevent infection becoming established in a colony and can be used in conjunction with treatment where infection is already present.

Feline leukemia virus (FeLV) infection

This virus is widespread and infection of outdoor cats or cats in infected catteries is common. The vast majority of persistently infected cats will die either from tumors or as a consequence of the immunosuppression caused by the viral infection. Current vaccines provide a good level of protection and do not interfere with routine testing for the virus in breeding colonies. Because the virus tends to take many months before it causes disease, infected cats can appear completely normal and healthy. For this reason your veterinarian may suggest your cat have a blood test to make sure it is not infected before vaccination. Despite vaccination, a few cats will still become infected with the virus.

Feline Infectious Peritonitis (FIP)

This is an uncommon disease although cases occur from time to time almost everywhere but infection with the causative and related viruses (coronaviruses) are common. We do not understand why a few infections lead to fatal disease whereas the majority cause minor illness. Vaccines are advised in some cases. Discuss usage with your veterinarian.


This is such an important disease because of the almost 100% fatality rate of cases once symptoms occur, and because of its potential transmission to people by bites from infected animals. Rabies vaccination is an essential part of the vaccination program for all cats.

Which vaccines are needed in dogs?

Depending on your locality some infections may be more or less likely. Your veterinarian will assess the relative risks based on your circumstances and advise you accordingly.


This disease affects all mammals and is spread by a bite or a scratch from an infected animal. It affects the brain and is often fatal. Bats are common carriers. The last locally confirmed case of rabies was a cat in Okotoks in November 2018. Two members of the family also had to be treated for rabies after they were bitten by the infected cat.


Highly contagious and spread through coughs, urine and feces of infected animals. Puppies are the most susceptible. Causes vomiting, diarrhea, seizures, and often death. Surviving dogs often suffer with neurological issues for the rest of their lives


A highly contagious and very hardy virus that is spread by direct contact with an infected dog, or indirectly, by the fecal-oral route. Heavy concentrations of the virus are found in an infected dog’s stool, so when a healthy dog sniffs an infected dog’s stool, it will contract the disease. The virus can also be brought into a dog’s environment by way of shoes that have come into contact with infected feces. There is evidence that the virus can live in ground soil for up to a year. It is resistant to most cleaning products, or even to weather changes. It attacks the intestinal tract causing bloody diarrhea and vomiting. Puppies are very susceptible to this virus.

Adenovirus type 1 (infectious canine hepatitis)

Transmitted through contact with infected feces and body fluids from infected dogs. This disease progresses very quickly causing fever, coughing, bloody diarrhea, abdominal pain and liver failure

Canine Cough/Parainfluenza

Caused by adenovirus type 2. A respiratory disease which causes a hacking cough, fever and sometimes a runny nose and pneumonia. Often found in places where large numbers of dogs gather i.e. dog park, daycare, boarding kennels, groomers. It is an airborne virus so even dogs that don’t go to the dog park can contract the virus. There are many strains, like the human cold or flu virus.


Spread by infected urine which dogs can come into contact with directly or indirectly through water or contaminated soil. It is zoonotic. Commonly spread by rats and so is not prevalent in Alberta but vaccine may be required if pet is travelling. Symptoms include muscle pain, vomiting, diarrhoea, loss of appetite, depression, jaundice and blood clotting problems.

Lyme disease

Transmitted by infected ticks it often causes lameness due to swelling in the joints and depression. It can also cause damage to the kidneys. This is very difficult to treat and is often incurable.

Booster vaccines – are they really necessary?

Primary (puppy and kitten) vaccination is essential in order to prevent the once common kitten and puppyhood fatal diseases from returning. However, recent research indicates that all vaccines may not require yearly booster vaccines.

Vaccines made for viral diseases tend to have a longer duration of immunity than bacteria based ones, which typically require annual revaccination.  These simply do not confer longer term immunity.

If you have any concerns in this area please do not hesitate to discuss them with us. The problem is one of risk and benefits. There is no evidence that annual booster vaccination is anything but beneficial to the majority of pets. To establish whether boosters are really necessary, blood tests to measure the amount of antibodies present in your pet are necessary. Unfortunately, these are usually more stressful and certainly more expensive than a simple revaccination. Published research has shown conclusively that omitting to re-inoculate against some of the major diseases can put pets at risk.

Vaccines are regulated and vaccine manufacturers must prove that the vaccine is safe and effective before it can be used in your pet. Through vigilance and high standards, the veterinary vaccines used today are the safest and most protective ever.

I would prefer my pet to have boosters only when necessary. Is this possible?

Yes and no. Titre checks are blood tests done in a lab setting which estimate the ability of antibodies in the blood to neutralize a dose of virus.  These can give a good estimation of the potential of still having adequate immunity to not require revaccination.  They are not 100% indicative of what will happen in the body, as the body is not as fully controlled a setting as a lab beaker!  So, yes we can check a titre, but it may not be a perfect correlation.  Other considerations:  the cost of the blood test is likely to be more expensive than the vaccine itself, and some vaccines only are available in combination with other constituents. From your pet’s point of view, it is preferable to receive one injection against the common diseases rather than a series of single disease inoculations as they individually become in need of boostering.

Deciding which vaccinations your pet receives should be based on your pet’s lifestyle, age and health status. Our trained veterinary healthcare team can help guide you through this decision-making process to ensure that your pet receives the highest standard of care and protection.

Why does my pet need an annual exam if it doesn’t need vaccines?

The annual health examination is about so much more than vaccines.  It involves a thorough health check – ears, eyes, heart, lungs, joints, teeth, and behaviour. Diseases of these areas, and other problems, are frequently detected during this examination and can be successfully treated because of early diagnosis. It also provides a time to discuss current health issues like parasite prevention and life stage needs, which change with age for each pet.