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Ask a scientist
In this feature, NRC scientists answer questions about biology, chemistry, physics, astronomy and other science topics.
Question: What are vaccine adjuvants and are they safe for pregnant women?
Answer: Adjuvants are substances added to vaccines to help them work better. In fact, the word "adjuvant" comes from the Latin adjuvare, meaning "to help." Adjuvants are also referred to as immuno-stimulants because they trigger the immune system to become more receptive or sensitive to the presence of a vaccine.
Vaccines work by teaching your immune system to recognize a particular organism and fight it off — without you having to get sick. They are generally made from weakened or killed forms of a pathogen, or sometimes just part of a pathogen called an antigen. On their own, many pure vaccines aren't quite strong enough to stimulate the immune system to protect you from future infections. So, adjuvants are added to give things a boost.
Aluminium salts (aluminium phosphate and aluminium hydroxide) are the most commonly used adjuvants in vaccines. Called "alum" for short, they have been used for this purpose since the 1930s. Alum causes a small amount of inflammation, triggering the immune system to become a little more "excited" so that it better recognizes the specific pathogen that is being introduced to it.
Researchers are investigating other types of adjuvants that would stimulate the immune system in different ways than alum does. There are various diseases for which vaccines are ineffective, such as AIDS, and scientists hope that new types of adjuvants might help overcome this problem.
Because adjuvants make vaccines so much more effective, many vaccines can be given at a lower dose. Before any vaccine or adjuvant is approved for use, it must go through rigorous studies to determine it is safe for use in humans. Adjuvants degrade and eventually are eliminated from the body.
How adjuvants work
What does all this mean for pregnant women? The answer: it depends. Risks and benefits must be weighed when deciding whether or not to get vaccinated. In some cases, the potential dangers of getting a specific disease outweigh the risks from vaccination.
The U.S. Centers for Disease Control recommends that vaccines be used in pregnant women only if:
- a specific vaccine is not considered harmful to pregnant women and their fetus;
- exposure to disease risk for mother and fetus is high; or
- the resulting infection from disease would be a danger for mother or fetus.
When it comes to specific vaccines, the general rule is that the bigger the immune response a vaccine causes, the riskier it may be for a pregnant woman. Live vaccines are generally not recommended during pregnancy. Measles, mumps and rubella are examples of live vaccines.
Seasonal flu shots (if made from killed viruses) are often recommended for pregnant women because getting the flu could have damaging effects on the fetus. There are some vaccines for which the safety in pregnancy is unknown. It's always best to consult your physician.
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