Why the 'Born Before 1957' Rule Exists
For decades before the measles vaccine was introduced in 1963, measles was a common and widespread childhood disease. Nearly every child would contract the measles by the age of 15. Because of this high prevalence, individuals born in or before 1956 are considered to have had natural immunity from prior infection, which is generally lifelong. This is known as presumptive immunity. The CDC uses 1957 as the cutoff year for this presumption.
However, this rule comes with a few important caveats. First, healthcare workers are typically an exception to this presumption, as their increased risk of exposure necessitates documented proof of immunity or vaccination, regardless of their birth year. Second, if an adult is not sure about their vaccination history, the CDC recommends getting vaccinated, as there is no harm in receiving another dose if you are already immune.
Factors Affecting Immunity in Adults
Several factors can influence an older person's immunity to measles. Natural infection or full, modern vaccination typically provides lifelong protection, but a few specific scenarios can affect an adult's immune status. The effectiveness of early vaccines and different immunization strategies for special populations all play a role.
Inactivated (Killed) Vaccine
During the early years of the measles vaccine rollout (1963–1967), an inactivated, or "killed," measles vaccine was used. This version was later found to be less effective at providing long-term immunity than the live attenuated vaccines that followed. Individuals who received this killed vaccine during that period, or a vaccine of unknown type, should be revaccinated with at least one dose of the modern live attenuated MMR vaccine. A blood test, known as a titer, can also determine if they have sufficient antibodies.
Breakthrough Infections
Even with modern vaccines, a small percentage of fully vaccinated individuals (about 3%) may experience a breakthrough infection if exposed to the virus. For these individuals, the symptoms are typically much milder and they are less likely to spread the virus to others. However, the occurrence demonstrates that vaccination doesn't guarantee 100% protection, though it significantly reduces risk and severity.
Comparing Sources of Measles Immunity
| Feature | Natural Infection (Born Before 1957) | Live Attenuated MMR Vaccine (Standard) | Inactivated (Killed) Vaccine (1963-1967) |
|---|---|---|---|
| Mechanism of Immunity | Wild-type virus exposure creates lifelong immunity through natural disease. | Introduces a weakened, live virus to prompt a robust immune response. | Administers a non-infectious, killed virus; provides less robust, shorter-term immunity. |
| Protection Level | Generally considered lifelong and highly effective. | Highly effective, with 97% protection after two doses. | Poor long-term efficacy, requiring revaccination with the live version. |
| Documentation Needed | Birth year verification is sufficient for most non-healthcare settings. | Official vaccination records showing one or two doses after age 1. | Revaccination with the modern live vaccine is needed due to limited efficacy. |
| Risk Group Exception | Healthcare personnel born before 1957 are not presumed immune and must show documentation. | Some adults in high-risk groups (travelers, healthcare) need two doses. | Individuals in this group are at higher risk and require a re-immunization. |
Why Measles is a Concern for Vulnerable Adults
While natural immunity offers strong protection, not all older adults fall into this category. Beyond vaccine history, other risk factors come into play, especially when considering the severity of the disease. Measles can be a serious and potentially deadly illness, and older adults are among the groups at higher risk for complications, along with young children and the immunocompromised.
Increased Risk of Complications
For adults over 20, the risk of serious complications like pneumonia and encephalitis (brain swelling) increases significantly. Pneumonia is the most common cause of death from measles in young children, but adults are not spared. About one in five unvaccinated people in the U.S. who get measles are hospitalized. Encephalitis can cause lasting brain damage or death.
Immune Amnesia
Recent research highlights another long-term danger of measles: immune amnesia. The virus can wipe out the body's memory of previous infections, essentially resetting the immune system and leaving an individual vulnerable to diseases they were previously immune to. This effect can last for years and is a concern for people of all ages who contract the virus.
How to Determine and Boost Your Immunity
If you're an older adult and unsure of your immunity status, a conversation with your healthcare provider is the best course of action. They can help you determine the appropriate steps for protection.
How to Check Your Immunity
- Find Records: Check for documentation of your vaccination history, especially if born after 1957.
- Laboratory Evidence: A blood test called a titer can confirm if you have protective antibodies against measles. However, experts often recommend simply getting another dose of the MMR vaccine instead, as it is safe and can eliminate the need for a blood draw.
When to Consider a Booster
- Healthcare Workers: All healthcare personnel must have documented evidence of immunity, regardless of birth year.
- International Travelers: If you are traveling outside the U.S., it's wise to ensure full vaccination.
- Exposure to Outbreaks: During a local outbreak, public health authorities may recommend revaccination, especially for those in high-risk environments.
Conclusion
While many older individuals born before 1957 benefit from natural immunity, the blanket assumption that all seniors are safe from measles is false and potentially dangerous. The history of the vaccine, particularly the less-effective early versions, means some adults may have insufficient protection. Combined with the higher risk of complications in older age and the threat of immune amnesia, it is essential for older adults to verify their immunity, especially those in high-risk professions or with uncertain vaccination records. Consulting a healthcare provider is the most reliable way to ensure you are fully protected against this highly contagious and serious disease. Public health relies on high vaccination rates across all age groups to protect the entire community.
