One of the greatest frustrations occurs when a dog develops a disease against which it has been vaccinated. There are five possible reasons for this.
1) Ineffective vaccine
The vaccines made by federally licensed manufacturers are potent at the time they leave the factory; however, several things may happen to inactivate them. The most common cause of vaccine inactivation is that the vaccine has been allowed to become too warm. Temperature is critical in maintaining potency. If the vaccine becomes too warm during shipment to the distributor or while being stored at the distributor, it is inactivated.
"Temperature is critical in maintaining potency."
This is a common problem associated with vaccines purchased by internet, mail order, or from feed stores. The buyer has no way to determine whether the vaccines were handled properly during shipment to non-veterinary suppliers. Veterinarians routinely refuse to accept shipments of vaccine if the vaccine is warm at the time of arrival.
It should be noted that the opposite problem can also occur if a vaccine is handled incorrectly. The vaccine can become "virulent", or cause the infection which it is intended to prevent.
2) Inherent characteristics of the vaccine
Although most of our vaccines have a very high success rate in dogs, none produces immunity in 100% of the dogs being vaccinated. While vaccine programs are designed to maximize immunity, it is important to recognize that they do not provide 100% immunity against the disease.
3) The dog is not healthy when vaccinated
"It is essential that the dog's immune system is functioning properly."
It is essential that the dog's immune system is functioning properly in order to respond appropriately to a vaccine challenge. If the immune system is immature, it cannot do so. If the dog has a disease that suppresses the immune system, it will not respond. If the dog has fever, the immune system will be so "occupied" with the fever that it will respond poorly to vaccine. It is important to discuss any health concerns with your veterinarian prior to vaccination.
4) Breed differences
Certain breeds of dogs appear to be especially susceptible to certain viruses. This has been observed for years, but recently it has been most obvious in Rottweiler dogs and the canine parvovirus vaccine. A small but disproportionate number of Rottweiler puppies have reportedly developed parvovirus enteritis despite proper vaccination.
5) Interference due to maternal antibodies
When a puppy is born, it receives passive immunity from its mother in the form of maternal antibodies. Maternal antibodies protect the newborn from the diseases against which the mother was protected. Maternal antibodies only last a few weeks in the puppy; this duration is directly proportional to the level of immunity the mother has. If her immunity level against rabies, for example, is very high, the maternal antibodies for rabies may last up to three months. If her level is low, they may persist only five or six weeks. As long as they are present, the puppy is passively protected; however, those antibodies also block a vaccine challenge. If a puppy receives a vaccination for rabies before the maternal rabies antibodies are gone, the vaccine's effect is blocked, and little to no immunity develops. The same holds true for the other components of the vaccines; temporary immunity received from the mother can interfere with all of the vaccinations.
Parvovirus seems to provide maternal immunity that lasts for quite a long time, up to four months in some dogs. For this reason, your veterinarian may recommend an additional parvovirus booster vaccination, given after the puppy series of vaccinations has been completed, usually at about 18 to 20 weeks of age.
"In an ideal situation, a vaccination would be given just before the maternal antibodies are completely gone, but before the puppy is exposed to the disease-causing virus or bacterium."
In an ideal situation, a vaccination would be given just before the maternal antibodies are completely gone, but before the puppy is exposed to the disease-causing virus or bacterium. However, it is not practical to determine just when the maternal antibodies are gone for each of the possible diseases. Although it can be done, it is costly. If the maternal antibodies have waned and the pet is exposed to the disease-causing virus or bacterium before vaccine-induced protection has developed, the puppy will usually develop the disease.
The current solution to this dilemma is to give a series of vaccinations on a pre-determined schedule, usually every three to four weeks. This series of vaccinations is successful in the vast majority of situations. In special circumstances, such as if the pup's environment is known to be infected with a particular disease-causing agent, your veterinarian may recommend vaccinating every ten to fourteen days from age six weeks to twenty weeks. The disadvantage for such a plan is the expense. Instead of giving three vaccinations in the series, the veterinarian would be giving six or eight; thus, the cost would be considerably greater. Your veterinarian can discuss the potential benefits and risks of extra vaccinations in these special circumstances.