Measles IgG Antibody Waning After Single MMR Dose
No, you should still give the second MMR dose because waning immunity is NOT a major cause of vaccine failure—the primary issue is that approximately 5% of children fail to develop immunity after the first dose (primary vaccine failure), and the second dose is specifically designed to protect these non-responders. 1
Why the Second Dose Matters
The ACIP explicitly states that waning immunity has little influence on measles transmission, and the major benefit of the second dose is reducing the proportion of persons who remain susceptible due to primary vaccine failure. 1
Key Evidence on Antibody Dynamics
Antibody levels can decline over time without loss of immune memory, meaning low or negative titers do not indicate true susceptibility in properly vaccinated individuals. 2, 3
Research shows that among children who received only one MMR dose, 12.1% demonstrated primary vaccine failure for measles, and an additional 4% responded initially but became seronegative within one year. 4
Even when measles antibodies wane, protection against disease is largely retained through immune memory mechanisms. 5
What Happens Without the Second Dose
Approximately 16-25% of children lack demonstrable measles antibodies one year after a single MMR dose, combining both primary vaccine failures and those with waning antibodies. 6, 4
Among two-dose recipients followed for 10 years, 93.7% maintained protective measles antibody levels, demonstrating the durability of immunity after proper vaccination. 5
Almost all children who do not respond immunologically to the first dose will develop measles immunity after receiving a second dose. 1
Clinical Bottom Line
The second dose is not primarily a "booster" for waning immunity—it's a safety net to catch the 5% who never responded to the first dose. 1 While some antibody waning does occur, revaccination of children with low measles antibody levels produces only a transient rise in antibody levels, confirming that the second dose's main value is addressing primary vaccine failure, not boosting waning immunity. 1
The two-dose MMR schedule is designed to capture primary vaccine failures, and individuals with two documented doses are considered immune regardless of subsequent serologic testing results. 2, 3