Question 9 of A Parent’s Guide to Vaccines: A Conversation About Vaccines for New Parents

A titer is a ratio used to explain the amount of something in a solution. When talking about vaccines or immunity to disease, titers identify the amount of antibodies in a person’s blood.

Antibodies are proteins that can be found circulating through your body. It is their job to find and remove potential pathogens like viruses and bacteria.

Detecting the types and amount of circulating antibodies can tell your doctor:

If you are immune to a disease (IgG)

If you actively have a disease (IgM)

If you are having an allergic response (IgE)

Titers are important because you could have been exposed to a disease, not shown symptoms, and developed immunity without even knowing it. This can be the case for some vaccine preventable diseases like chickenpox or measles. When this happens, vaccination is unnecessary, because your body is already protected.

In other cases, titers are important because you may have become immune to a disease after one vaccine dose, when two or more are required. This is the case for 93% of the population who become immune after one dose of the measles, mumps, and rubella (MMR) immunization. Only about 7% of vaccinated individuals actually need the second dose to complete immunity, according to the CDC.

The goal of the national vaccination program is not to simply increase vaccination rates, but to create immunity to potential diseases. If your titers show that you are already immune, you may not need another vaccine dose for that disease.

Remember, immunity is not always permanent. If your titers show that you are currently immune, you may need to be retested again in the future to ensure that you have retained that immunity.

A Side Note: Titers, MMR, and New Jersey In New Jersey, parents have the option to have their child tested for titers that would show immunity to MMR before getting vaccinated a second time, and opt out of the second vaccine if the test comes back showing an adequate amount of antibodies. This option is actually a law, nicknamed Holly’s Law, after a NJ family lost their daughter from an adverse vaccine reaction to her second MMR vaccine, a requirement for her to attend kindergarten. The logic behind Holly’s law is that those who are already immune from their first vaccination no longer need to be vaccinated.

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