A Compilation of Notes on Puppy Vaccinations

Before discussing vaccines, let's first talk about immunity and its basic types. Baidu Baike defines human immunity as follows: immunity is a physiological function of the human body, by which the body can distinguish "self" from "non-self" components, thereby destroying and rejecting antigenic substances that enter the body, or damaged cells and tumor cells produced by the body itself, in order to maintain the body's health. It is a state of resistance to or prevention of infection by microorganisms or parasites, or other undesired biological invasions. Immunity involves both specific and non-specific components. The non-specific components do not require prior exposure and can respond immediately, effectively preventing invasion by various pathogens. Specific immunity develops over the host's lifetime and is targeted against a particular pathogen. The basic principles of immunity in dogs and humans are roughly the same. From a professional standpoint, vaccinating a dog means establishing specific immunity within the dog's body to respond to common viral infections such as canine distemper, parvovirus, and parainfluenza. It is commonly said that a dog's immunity lasts one year and that vaccination must be repeated every year. According to the principle of specific immunity, this suggests that the memory cells of canine cellular and humoral immunity live only a little over a year. A vaccine is an auto-immune agent made from microorganisms (bacteria, rickettsiae, viruses, etc.) and their metabolites, after artificial attenuation, inactivation, or transgenic methods, used to prevent infectious diseases. After a person or animal is vaccinated, the specific immune system in the body is activated; through immune organs and immune cells, antibodies and effector T cells are produced, followed by memory cells. When the body is invaded by the same virus again, the memory cells respond immediately, the immune system kills the antigen, and immunity is achieved. The reason why each dose in a puppy's initial vaccination is separated by 2-3 weeks is probably because it takes 14-21 days in total for the puppy to go from vaccination to a complete immune-system response. (As shown later, this conclusion is wrong. That time is the interaction window between maternal antibodies and the attenuated virus.) Among the imported vaccines currently popular on the market is "Nobivac" (英特威); the full English name of its quadruple vaccine is "Canine Distemper virus, Adenovirus, Parvovirus, Parainfluenza virus Vaccine, Live". From "Live", we can see that this vaccine is a live, artificially attenuated vaccine. If a puppy is in an unhealthy state, administering this vaccine may actually cause infection by viruses such as parvovirus and canine distemper. Regarding the type of vaccine for puppies, such as choosing domestic or imported, or a quadruple versus an octuple, there are already fairly mature conclusions. However, there is significant disagreement about the timing of a puppy's first injection. In summary, there are roughly the following approaches: 1. After the puppy is weaned at 28 days, when its own immune system is not yet mature, first inject a bivalent, pentavalent serum, or a monoclonal antibody to obtain short-term immune protection, and 21 days later, proceed with the standard vaccination schedule. 2. The puppy acquires maternal antibodies from breast milk, and usually around 8 weeks (56 days) the antibody concentration falls below the level required for immunity. Antibodies effective against "parvovirus" and "canine distemper" are no longer sufficient to resist these two viruses at 6-7 weeks (42-49 days), because other antibodies are still active at that point. Therefore, the Nobivac bivalent (parvovirus and distemper) should be given at 42 days, and the quadruple or octuple at 8 weeks. 3. Give the first injection around 6-8 weeks (42-56 days) of age, the second 21 days later, and the third 21-28 days after that. However, if the last injection finishes before 15 weeks (105 days), a fourth injection is required. Baidu Baike defines maternal antibodies as follows: antibodies that come from the mother. Maternal antibodies can be transferred to the embryo via the placenta or colostrum, giving the newborn protection. But the presence of maternal antibodies interferes with and reduces the newborn's immune response to the primary vaccination, thereby weakening the effect of the primary immunization. Therefore, one generally waits until maternal antibody levels are low before performing the primary immunization. Mammalian colostrum contains a large amount of antibodies. Newborn mammals are not fully developed, are poorly adapted, and have low resistance to adverse external environments. After young animals ingest colostrum, they can immediately acquire maternal antibodies, increasing their resistance, and suppressing conditioned disorders caused by opportunistic pathogens. The antibody content in colostrum drops rapidly 12 hours after birth, and the ability of the young animal's intestinal mucosa to absorb antibodies also gradually decreases over time; by 24 hours, absorption is nearly impossible. Therefore, ensuring that young animals ingest colostrum within 24 hours is key to their survival rate. From the above, we can understand that if a puppy has high levels of maternal antibodies, after vaccination the maternal antibodies will kill the attenuated virus in the vaccine, rendering the vaccine ineffective. At the same time, the killed attenuated virus will lower the maternal antibody level, weakening the puppy's resistance. Suppose the maternal antibodies are no longer sufficient at week N to cope with parvovirus and distemper infection, and by week M the maternal antibodies are at an immunological disadvantage. From the perspective of biological evolution, this time must coincide with the puppy's immune system becoming initially mature. Administering the first vaccine during this period is more reasonable and appropriate. Since maternal antibodies are only present in the mother's colostrum, after 24 hours the maternal antibodies in the puppy should be on a downward trend at some unknown rate. At this point, maternal antibodies are still present in the puppy's body at low levels, and injecting a vaccine will at worst cause the attenuated virus to completely neutralize the maternal antibodies and overwhelm the existing, initially established immune system; in other words, the puppy dies of viral infection. Let's simplify with another assumption: the amount of a single virus that the maternal antibodies in the puppy can kill is X, the amount of a single virus that the initially established immune system can resist is Y, and the total amount of a single virus in the vaccine is A (X>=0 && Y>=0 && A>0 && X*Y>0). When A>=X+Y, immunization fails and the puppy dies; when A<=X, immunization fails and specific immunity against the virus is not established; when A>X and A<X+Y, specific immunity against the virus is established and immunization succeeds. Generally, a puppy needs three to four injections (bivalent, quadruple, hexavalent, or octuple) to achieve immunity. From the above, the conclusion is that the last injection falls into the A>X && A<X+Y category. Since cases of puppies dying from the first vaccine injection are rarely heard of, and given that the response of the initially established immune system to the attenuated virus cannot be assessed, the amount of attenuated virus in the vaccine must be very conservative—so conservative that we can boldly assume the first injection is entirely to neutralize the maternal antibodies (A<X). So from this point of view, a bivalent injection at this point is more conservative, while the octuple is rather aggressive, but the A>=X+Y outcome should not occur. For the second injection, if 2*A is much greater than X, it will still cause unknown consequences to the puppy's fragile immune system. We can deduce A≈0.5X: on one hand, further neutralize maternal antibodies; on the other, continue to observe and lightly stimulate the puppy's own immune system. So by the third injection, X≈0, the immune system responds, and immunization succeeds. Revisiting the three vaccination schedules proposed earlier, the first approach actually extends the time during which X exists, but X will eventually be 0, so it is completely unnecessary. The second puts the cart before the horse: before immunity is complete, one should try to keep the rearing environment safe, rather than over-pressuring the initially established immune system, and the first bivalent injection only partially neutralizes the maternal antibodies. The third approach comes from a Tieba post, and the inquiry into maternal antibodies also originated from there. The post emphasizes completing the final injection after 15 weeks, from which we can infer that a puppy's immune system is essentially fully developed at around 15 weeks.