In contrast to active immunity, like when you get a vaccine, passive immunity isn’t triggered by your own immune system.
Instead, passive immunity is the protection you can get from “someone” else.
Passive Immunity is Temporary
While the best example of passive immunity is the protection that newborn babies get from their mothers, other examples include:
- antitoxin serum – often produced in animals, this type of serum can provide antibodies against botulism and diphtheria toxins. Examples include TAT, DAT, and HBAT.
- immune globulin – either pooled or from a single person with high titers of antibodies, immune globulin is made from donated plasma can provide antibodies against the hepatitis A or B virus, measles, rabies, tetanus, and varicella. They can be used for postexposure prophylaxis, after you have been exposed to one of these diseases and are not already immune. Examples include IGIV, HBIG, VariZIG, RIG, and Baby BIG, etc.
- palivizumab (Synagis) – a monoclonal antibody that is specific for the RSV product and which is given to high risk premature babies to keep them from getting sick during RSV season.
Again though, the best example of passive immunity is the transfer of a mother’s antibodies to her baby through her placenta, which can include antibodies against measles, pertussis, and hepatitis B, etc., as long as the mother has immunity to these diseases.
Of course, this type of passive immunity doesn’t mean that your baby doesn’t need to get vaccinated, a common argument of those who skip or delay getting their infants vaccinated.
The biggest problem with passive immunity is that it is only temporary. In the case of maternal antibodies, they start to wane after a few months in many cases, even though they might provide protection against many diseases for up to six to twelve months.
Polio and Passive Immunity
Passive immunity likely helped prevent young children from getting more serious cases of polio in the pre-epidemic era. While infants likely got exposed to polio when they were 6 to 12 months old, since they still had partial protection from maternal antibodies, they may have gotten diarrhea (enteric infection), but it wouldn’t progress to the more serious paralytic polio.
With better hygiene and sanitation, eventually fewer young infants got exposed to polio, and we lost this method of getting “active immunity under the cover of passive protection.” Instead, they got exposed when they were older and had lost any protection from passive immunity. This led to the epidemics of polio and paralytic polio with which we are all familiar.
Breast milk is another source of passive immunity. This comes from a different type of antibody though, in addition to other substances in breastmilk. While the antibodies babies get through the placenta are IgG antibodies and are directed against most vaccine-preventable diseases, breastmilk antibodies are IgA.
IgA is also called the secretory immunoglobulin, as it is found in our saliva, and respiratory tract and intestinal secretions, but don’t enter our bloodstream. While the secretory IgA antibodies children get in breastmilk won’t protect them against most vaccine-preventable diseases, they can protect them from other viruses and bacteria that cause diarrhea and respiratory infections, etc.
For More Information On Passive Immunity:
- Maternal Antibodies: Clinical Significance, Mechanism of Interference with Immune Responses, and Possible Vaccination Strategies
- How long do babies carry their mother’s immunity?
- Passive Immunity 101: Will Breast Milk Protect My Baby From Getting Sick?
- From Emergence to Eradication: The Epidemiology of Poliomyelitis Deconstructed
References On Passive Immunity:
Vaccines (Sixth Edition), 2013