In this column veterinarian Dr Liesel van der Merwe provides practical assistance for common problems in companion animals. She is a specialist physician at the Onderstepoort animal teaching hospital and a senior lecturer in the section of small animal medicine. Send your questions to This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Dr Liesel van der Merwe

Iam going to try and demystify the whole vaccination process for all you pet owners out there. This will involve me taking some liberties with the exact detail of the immunological process, so to those with a bit more knowledge on the subject, please bear with me.

Antibodies are the “tracker system” of the body. They are a kind of protein designed to identify only specific foreign substances, such as viruses, bacteria or protein particles in allergies.

Each pathogen thus has a specific antibody. Once they have identified an “intruder”, they attach to it and flag it for the immune system cells, which then engulf the foreign substance and process it to activate the immune system.

Young animals are not born with their own antibodies; these only develop with time due to exposure to the environment and pathogens. In humans, the placenta allows mixing of maternal and foetal blood and a baby is born with its mother’s antibodies in the blood to ensure early protection.

The placenta in animals is not as intimate and blood is not shared. Young animals rely on antibodies which have accumulated in the first milk (colostrum). Milk contains high levels of antibodies throughout lactation in cats, but antibody levels drop rapidly in other species.

The stomach is normally impermeable to proteins and the acid would normally digest proteins but in the first 12-24 hours after birth there are gaps in the stomach lining, allowing antibodies to be absorbed into the bloodstream of the newborn. These then provide protection in the first six weeks of life. It is thus vital that newborn animals suckle within the first 12-24 hours of life.

All proteins in the body have a lifespan and are recycled, and these antibodies start decreasing so that at about six weeks of age they are no longer very protective. This is when vaccination plays a role. Vaccinations are either a “dead” form of the virus or bacteria, a modified live or weakened form or a reconstituted vaccine which uses only a part of the virus.

Vaccination hardly ever causes disease in dogs and cats although they can in animals such as the wild dog, panda and other wild canidae and felidae.

The first vaccine can only be given once the maternal antibodies are decreasing, otherwise they will identify the vaccinated pathogen and block the immune response. This is why we generally give the first vaccination at six weeks. If there is a problem with a disease in a kennel, we can start at four to five weeks.

This first vaccine primes the body against the disease. The body has to identify the pathogen as foreign, without the benefit of antibodies, as they are not yet present, and present it to the cells of the immune system, which will make specific antibodies, and make memory cells against that specific pathogen. This whole process takes about three weeks and is called seroconversion. The reason for the booster four weeks afterwards and again four weeks later is to remind the immune system and thus really establish a good memory.

In some cases it can also be argued that the maternal antibodies may still interfere with the six week vaccination, so we are really trying to cover all bases. The rabies vaccination is usually delayed until after three months, as maternal antibodies interfere with the vaccination if the puppy is younger.

The booster at one year is important to set the memory as well as boost the rabies vaccination. The duration of the immunity or memory of the body is different for different organisms – it is long lasting against rabies, but shorter against snuffles or kennel cough. Thus each individual animal has a different antibody profile depending on their exact environment and vaccination status.

The response of a vaccinated animal to a virus is much quicker, as the virus is identified earlier and memory exists. Antibodies are quickly made as the “recipe” is already known, whereas in an unvaccinated animal the immune system first has to identify the virus without the help of antibodies, break the virus into bits to find the recipe required to identify it again and then programme cells to make this antibody. This time lag will allow the infection to become established in the body. Vaccinated dogs are primed to identify and destroy, thus preventing establishment of infection.

Vaccinations do not work very well in dogs which are malnourished and in animals with a compromised immune system and drugs such as chemotherapy and cortisone will also reduce efficacy.