Maternal vaccines are given to pregnant females to protect their offspring from infectious diseases. Administering specific vaccines during late pregnancy harnesses the ancient evolutionary mechanism by which dams pass on antibodies to their neonates.
Antibodies generated by pregnant females are fully formed and functional when they enter the blood stream of the offspring and give passive protection against viruses, bacteria and other pathogens. Antibodies from the dam bide time between birth and development of the neonate’s mature immune system.
At birth, neonatal animals have an immature immune system that has difficulty warding off infections. And there are some infections that specifically target young animals, making the risk diminish with time.
This is the case with some of the neonatal diarrhea viruses such as rotavirus. For other pathogens, the window provided by maternal antibodies allows time for direct vaccinations in those young animals to take effect when the neonate’s immune system is matured.
For maternal antibodies to do this protective work, they actually have to get into the offspring. In livestock species, maternal antibodies are present in colostrum and neonates must consume adequate amounts of this first milk in the few hours immediately post-birth to reap the benefits.
In some species, such as dogs and cats, maternal antibodies pass through the placenta and are present in the colostrum.
Certain vaccines are administered to the pregnant female before giving birth so her immune system has time to produce the antibodies and secrete them in the colostrum. Usually four to six weeks is sufficient.
Maternal antibodies enter the blood of neonatal animals following ingestion of colostrum and circulate throughout the body, ready to bind to pathogens and prevent infections.
Vaccines used during pregnancy are typically killed vaccines rather than modified live versions to avoid unwanted effects on the fetus, such as abortion.
Generally speaking, if a pregnant animal has not been vaccinated before or if her vaccine history is unknown, it is usually advised to vaccinate them before breeding, then follow up with a booster during pregnancy.
There are few examples of the use of maternal vaccination to protect offspring in animals. Pregnant cows can be vaccinated before calving to protect calves from scours (diarrhea) caused by rotavirus, coronavirus, E. coli and Clostridium perfringens Type C.
Pregnant mares are frequently vaccinated against tetanus, eastern and western equine encephalitis virus, West Nile virus and rabies in the four to six weeks before foaling (a four-way plus rabies protocol). Sheep and goats are often vaccinated against bacterial pneumonia and clostridial diseases in the four to six weeks prior to lambing.
Human examples of the use of maternal vaccination strategies include vaccination against tetanus, influenza and pertussis to reduce the risk of these infections in newborn babies before they can be vaccinated against these pathogens directly.
While maternal antibodies are important for protection against infections, they also have a downside — they prevent young animals from developing their own immune responses.
The timing of when their protection tapers off is highly variable and depends on the amount of maternal antibodies received. The more maternal antibodies, the longer they last.
Even within a litter, the amount of antibody received varies. Testing for antibody levels is possible but generally not practical for larger numbers at the herd level. It is because of maternal antibodies that many vaccination programs involve booster shots so as to ensure all individuals receive a vaccination when they can respond.
For instance, puppy vaccination series to protect against canine distemper virus typically include three separate shots. These start at eight weeks of age and repeat at 12 and 16 weeks of age since the window when maternal antibody wanes is unknown for specific puppies.
One way around maternal antibodies is mucosal vaccines, most often in the form of intranasal vaccines. This vaccine type involves a squirt of liquid up the nose, such as the strangles vaccine for horses and the combination bovine respiratory vaccines. Intranasal vaccines stimulate a different type of antibody and appear to work even with high levels of maternal antibody in the blood stream.
Plans to vaccinate your pregnant animals should be made in consultation with a veterinarian to get the maximum benefit and ensure there is minimal risk.