Vaccination of Dogs and Cats (給您的寵物伴侶注射疫苗)

These notes were originally prepared by a veterinary surgeon for general guidance and information only. To obtain advice and treatment for your dog or cat you should consult your registered veterinary surgeon.


Hong Kong is potentially a high-risk area for serious infectious diseases of dogs and cats, especially canine distemper, canine parvovirus disease, feline panleucopenia, and feline respiratory diseases including calicivirus and rhinotracheitis. Also of significance are some other diseases such as canine parainfluenza virus, hepatitis/adenovirus, leptospirosis, kennel cough, feline leucaemia, and others. Vaccination is an important part of the measures to prevent certain infectious diseases in dogs and cats of all ages, and especially in young animals including puppies and kittens.

You should consult your registered veterinary surgeon for advice on what vaccines and when, and for the actual vaccination of your animal. Be early, not late. Don’t delay vaccination. Don’t delay getting vet advice.

Vaccination works by producing an immune response to the diseases vaccinated against, but usually only works if the animals are adequately and fully vaccinated up-to-date before exposure to the disease. It usually needs at least two or three doses of vaccine [sometimes more doses] to produce an adequate immune response. After these initial doses, boosters are needed every one to three years depending on the vaccines used and the potential disease risk. Ask your vet about vaccination for your pet.

If your animals will go into kennels or catteries, then you also have to comply with requirements of those establishments. If the animals might travel, then you have to meet all requirements for that.

Vaccination Timing

Current guidelines [e.g. WSAVA: World Small Animal Veterinary Association] emphasize the importance of effective vaccination courses for young puppies and kittens. This usually involves at least 3 vaccinations of young pups and kittens [e.g. at 8 weeks,12 weeks and 16 weeks of age] to be completed before a risk of exposure to disease. In very high risk situations, even more doses may be used [and with shorter intervals between doses], and may then start at an even younger age, sometimes using special vaccines designed for very young animals.

For adult animals of uncertain recent vaccination history, then usually at least two doses of vaccination are given about 3 to 4 weeks apart to start or restart the vaccination programme.

After the initial course of vaccinations, a booster vaccination about one year later is normal to keep up the immune response levels. After that, booster doses are usually given every one to three years depending on the vaccines and the risk of disease. Ask your vet.

A few special vaccines not widely used for pets in Hong Kong may have different booster frequency requirements, e.g. twice a year for some.

Vaccination Against Rabies [Anti-Rabies Vaccination]

All dogs in Hong Kong are currently required to be vaccinated against rabies by an authorized officer, and licensed [dog license], by the time they are 5 months of age. Your vet can usually tell you how old your dog is [puppy tooth eruptions etc]. The requirements for anti-rabies vaccination, dog licenses and microchips are set out in the Laws of Hong Kong [Rabies Ordinance and Regulation, Cap421]. Most registered veterinary surgeons in Hong Kong, as well as some government officers, are authorized officers for this. Read and check all paperwork carefully.

All dogs must also be individually identified with a microchip implant under government rules and laws. The microchip is about the size of a grain of rice and is inserted under the skin with a special instrument. A special microchip reader [“scanner”] is used to read the identification information in the microchip. Normally one microchip will last the entire life of the dog. Hong Kong currently normally uses encrypted AVID microchips.

The anti-rabies vaccination and related issue of a new dog license must be repeated at least every 3 years [triennial revaccination and license renewal]. Keep your records carefully and don’t forget to renew in good time.

Any dog without a current valid dog license should be revaccinated against rabies and licensed as soon as possible, without delay.

These notes are only for basic information. Check fully with your vet and/or with the government authority [AFCD].

Some cat owners choose to have their cats vaccinated against rabies and microchipped for identification even if not required by law for cats. [Note that cats in feral cat colonies (e.g. SPCA cat colony care) should be microchipped and vaccinated against rabies, as well as ear-tipped and spayed/neutered].

The purpose of the requirement for mass vaccination against rabies of all dogs and of feral colony care cats, as well as microchip identification, and spay/neuter of colony cats, is to create a population immunity barrier against rabies in order to keep Hong Kong free from rabies, as well as providing a degree of individual animal immunity. [Such a population programme gives much better protection than removing and destroying animals].

Don’t Unwittingly Buy A Sick Puppy Or Kitten

Hong Kong is regarded as a high risk area for series infectious diseases of dogs and cats. Very young animals are highly susceptible unless they have been fully and effectively vaccinated well in advance against the relevant diseases.

In the case of puppy mills, pet traders, stray kennels and catteries and so on, where many susceptible animals might pass through, the risk of the animal acquiring serious possibly fatal disease is higher. Later vaccination of a puppy or kitten will NOT stop the disease, and vaccination on the day of sale or shortly before may also fail. It is usually advisable to have the animal checked by your registered veterinary surgeon before you confirm to buy and before you hand over any money etc. Have your vet examine the animal beforehand, and take your vet’s advice. Don’t buy an animal on a whim.

Many dogs and cats of all ages, young, medium and older, are uncaringly abandoned by their owners. Instead of buying a pet, you can save an abandoned animal by adopting from a reputable charitable rescue center. You are advised to have veterinary checks carried out and ensure valid vaccination, health protection, and current valid dog license [if a dog].

How Vaccination Works

This is a very simplified explanation. In nature, when an animal is exposed to a diseased-causing organism such as a virus, the animal’s immune system responds to produce various immune defense responses within the animal. These responses may include antibody production and cell-mediated immune responses. If the animal survives the infection and recovers or remains well, then the animal’s immune system “memory” may “remember” the disease and the responses it has now “learned” so that in the event of future exposure to the same disease, the animal can produce a much faster response to block the disease. In vaccination, to explain the most basic concept, the veterinary surgeon administers a dose containing the disease-causing organism or a part of that organism which has been prepared in such a way that it should not cause disease but will produce an immune response. Booster vaccinations are needed to “remind” the animal’s internal immune system at appropriate time intervals and keep it “alert”.

A vaccination programme is only likely to be effective in protecting a previously non-immune animal if the vaccines are given well before the animal is exposed to the disease(s), usually two or more doses of vaccine well before the exposure.

An effective vaccination programme achieves beneficial results in a number of ways, including: 1) inducing a level of immunity in the individual animal, and 2) producing “population-immunity” [“herd-immunity”] if a sufficient percentage of the population is vaccinated.

  1. Individual Immunity. The process wherein the vaccine induces an immune response in the individual animal is outlined above in simplified terms. There are many reasons why a dose of vaccine may fail to produce an adequate response, and multiple doses are usually necessary. This is especially critical in young animals.
  2. Population Immunity [Herd Immunity]. A continuous and persistent vaccination programme within a population can produce “herd-immunity” [“population-immunity”] if a sufficient percentage of animals in the population are properly vaccinated. Figures and estimates vary, but always should exceed 80%, and closer to 100% vaccination coverage of the population may be needed. Population immunity [Herd Immunity] creates a population barrier to spread of the disease because it is harder for the disease organism to find enough susceptible animals to multiply itself and spread further. This vastly reduces the amount of the disease-causing organism [e.g. virus] in the area. This is probably why anti-vaccination proponents are able to keep their animals free from major diseases in countries where the prevalence of the disease is low due to mass vaccination of other animals there. However, this population immunity does not protect an individual unvaccinated non-immune animal if the disease-causing organism gets directly to that animal. Also note that herd-immunity in a population usually fails when the percentage vaccinated drops below the critical level. In Hong Kong, probably no animal vaccines have sufficient percentage cover yet to achieve a population immunity barrier to disease.

Is Vaccination Safe?

There have been reports that vaccines have been associated with side effects, with reactions ranging from allergic such as facial swelling and itching, to severe reactions associated with formation of cancerous tumors in cats. Vaccines have also been blamed at times for autoimmune diseases in dogs. It is likely that the number of pets that experience a reaction is very low, although it is difficult to find accurate data as some reactions might go unreported, or some reactions may be either falsely-associated, or not-associated with the vaccine. It has been suggested that some vaccine reactions may be as frequent at 1:1,000 to 1:10,000. Adverse reactions may be related to particular components of certain vaccines, such as adjuvants, preservatives, etc.

But … Vaccinations have saved the lives of millions of dogs and cats. Before the days of effective vaccines and vaccination programmes, dogs commonly died from distemper, hepatitis, leptospirosis, parvovirus and complications of upper respiratory infections, while cats died from panleucopaenia, respiratory infections, feline leucaemia, etc. Animals still do so die where effective vaccination programmes are not carried out. Anti-rabies vaccinations also help to protect animals and us from the threat of rabies.

Pets should not be over-vaccinated, but neither should they be under-vaccinated. The benefit of the vaccine must outweigh the risk of the vaccine. In Hong Kong, the benefits of vaccination are generally substantial. In contrast, insufficient vaccination has caused the deaths of many animals in Hong Kong. Vaccines save lives.

To determine what vaccines your pet needs, your vet will normally weigh the risk-benefit relationship that is relevant to your pet. Choose a registered veterinary surgeon you trust and ask him/her what he/she believes is best for your pet. Regardless, your pet should receive regular examinations by your vet.

Is Vaccination Effective?

As explained above, a vaccine must be properly administered at the right times in the right ways, well before [usually some weeks before] exposure to the disease, in a properly designed vaccination programme implemented to prevent the diseases vaccinated against. Vaccination is especially important for young animals. For most vaccines, one dose is not enough. Unprotected animals may be incubating the disease for days and weeks before it shows. Vaccination of an animal already incubating the disease will not stop the disease. Booster vaccinations are also needed from time to time. Vaccines can be quite delicate, and need to be kept under the correct conditions, usually refrigeration. In general, your registered veterinary surgeon is the best person to advise you on vaccination and other health matters for your animals, and the person who should administer the vaccines. Ask your vet.

Blood tests to measure antibody level responses to vaccination are available but are quite expensive. Blood samples usually have to be sent overseas for these tests. Few owners choose this approach because a booster vaccination is usually more cost-effective for owners.


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