Rubella, often known as German measles, is a viral infection that can cause a mild rash, fever, and swollen lymph nodes in most individuals. However, for pregnant individuals, rubella infection poses significant risks, potentially leading to severe birth defects in the developing fetus, a condition known as Congenital Rubella Syndrome (CRS). The rubella vaccine, typically administered as part of the Measles, Mumps, and Rubella (MMR) vaccine, is designed to prevent this disease. Vaccination is highly effective at preventing rubella. Despite its general efficacy, some individuals may find they are not immune to rubella after receiving the vaccine.
How Rubella Immunity Develops
The rubella vaccine works by introducing a weakened, or attenuated, form of the rubella virus into the body. This live-attenuated virus stimulates the immune system to produce specific protective proteins called antibodies without causing the full-blown disease. These antibodies, particularly Immunoglobulin G (IgG), are crucial for providing long-term protection against future rubella infections.
Most individuals develop a robust immune response after receiving one or two doses of the MMR vaccine. For rubella, one dose can be about 95% to 97% effective, with two doses offering nearly 99% protection against both measles and rubella. This vaccine-induced immunity is generally durable, with antibody levels often remaining high for many years.
Why Immunity Might Not Be Achieved
Despite successful vaccination, several factors can prevent an individual from developing or maintaining sufficient immunity to rubella. One common reason is primary vaccine failure, where an individual’s immune system does not mount an adequate response to the vaccine, even when it is properly administered.
This is a natural biological variability, meaning some individuals simply do not produce enough protective antibodies to achieve immunity. Another possibility is waning immunity, which occurs when antibody levels, initially protective, decrease over an extended period and fall below the threshold considered protective. While rubella immunity is generally long-lasting, antibody levels can decline over time for a small percentage of people, potentially leaving them susceptible.
Rarely, issues related to vaccine handling or administration can also contribute to a lack of immunity. Vaccines, including the MMR vaccine, are sensitive biological products that require specific storage conditions, such as maintaining a precise temperature range. Exposure to extreme temperatures or light can reduce the vaccine’s potency, making it less effective when administered. Incorrect injection technique, though uncommon due to strict protocols, could also lead to an insufficient immune response.
In some cases, particularly in infants, the presence of maternal antibodies can interfere with the vaccine’s effectiveness. Antibodies passed from the mother to the baby during pregnancy can neutralize the weakened vaccine virus, preventing the infant’s immune system from developing its own protective response. This interference is a known factor in early childhood vaccinations, which is why MMR vaccination is typically recommended at specific ages. Finally, certain blood products received around the time of vaccination can also temporarily interfere with the immune response.
Sometimes, the issue may not be a true lack of immunity but rather limitations in the testing process itself. An antibody test might yield a false negative result, or it could be performed too soon after vaccination, before the body has had sufficient time to develop a measurable antibody response. Equivocal results, where antibody levels are borderline, can also occur and might require retesting to confirm immunity status.
Confirming Your Immunity Status
To determine your immunity to rubella, healthcare providers typically use a blood test called serology. This test specifically measures the presence and concentration of rubella-specific IgG antibodies in your bloodstream.
A positive test result indicates that sufficient IgG antibodies were detected, meaning you are considered immune to rubella. Conversely, a negative result suggests that no or insufficient protective antibodies were found, indicating a lack of immunity. Sometimes, a test might return an “equivocal” or “borderline” result, meaning the antibody level is neither clearly positive nor negative, and repeat testing may be recommended. These tests are generally reliable, but a healthcare professional should interpret the results in the context of your medical history.
What to Do If You’re Not Immune
If you discover you are not immune to rubella after vaccination, the first step is to consult a healthcare provider. They can discuss your test results, assess your individual risk factors, and recommend the most appropriate course of action. Often, the primary recommendation for individuals found to be non-immune is to receive an additional dose of the MMR vaccine.
Many individuals who did not respond adequately to a previous dose will develop protective immunity after a second or even third dose of the vaccine. This re-vaccination is particularly important for women of childbearing age due to the severe risks of Congenital Rubella Syndrome (CRS) during pregnancy. Rubella infection during pregnancy, especially in the first trimester, can lead to severe outcomes like miscarriage, stillbirth, or significant birth defects.
After receiving an additional dose of the MMR vaccine, it is generally advised to avoid pregnancy for at least four weeks. This precaution is due to the vaccine containing a live, attenuated virus, though there have been no reported cases of CRS in women who unknowingly received the vaccine while pregnant. Reassuringly, receiving an extra dose of the MMR vaccine when you are already immune or partially immune is considered safe and does not pose a risk of harm.