Maternal Measles Antibodies Wane by 6 Months, Leaving Most Infants Susceptible
Maternal measles antibodies in newborns fell below the limit of detection by the time most infants reached 6 months of age, according to research presented at IDWeek 2026 on October 22.
- Fewer than 1 in 5 infants were seropositive for at least one measles strain at 6 months of age, leaving them vulnerable during regional outbreaks.
- Data from the Centers for Disease Control and Prevention show the US logged 5,182 measles cases as of November 6, alongside eight total deaths in Pennsylvania, New York, and Wisconsin.
- Researchers suggest evaluating earlier vaccination strategies, such as administering the measles-mumps-rubella vaccine at 9 months of age during periods of higher measles circulation.
Infant Antibody Levels Decline Faster than Previously Thought
According to Medscape, citing findings presented by C. Buddy Creech, MD, MPH, professor of medicine at Vanderbilt Medicine and pediatric infectious diseases director of the Vanderbilt Vaccine Research Program in Nashville, Tennessee, less than 1 in 5 infants tested positive for antibodies against at least one measles strain by the age of 6 months.
Creech told attendees that infants are going to be susceptible to measles virus infection sooner than previously thought, placing them at higher risk for pneumonia and later development of subacute sclerosing panencephalitis.
A multi-country study published in the Journal of Infection analyzed stored infant serum samples from 11 countries and found that maternal measles antibody decay rates remain consistent across different geographic settings.
Authored by researchers including Merryn Voysey and Karen S. Tiley, the analysis showed that geometric mean plaque reduction neutralization titers fell below the clinical protection threshold of 0.12 IU/mL between 2.5 months in Guatemala and 6.2 months in Pakistan. At age 6 months, fewer than 50% of infants maintained protective antibody concentrations in all evaluated countries except Pakistan.
Measles Incidence Reaches Highest Level Since 1991
The US is experiencing its highest measles incidence since 1991, with the count reaching 5,182 cases as of November 6, according to CDC data cited by Medscape. An estimated 94% of these cases occurred in individuals who were unvaccinated or had an unknown vaccination status, with roughly 1 in 5 cases affecting children younger than 5 years. CDC data from 2025–2026 show that only 10 US states reported at least 95% of kindergartens vaccinated with the measles-mumps-rubella vaccine.
As of November 8, eight deaths due to measles have been reported across three states, including six in Pennsylvania, one in New York, and one in Wisconsin. Medscape reported that all of these deaths occurred in unvaccinated individuals, several of whom were infants younger than 1 year.
Infant Antibody Levels Drop Significantly by 6 Months
In the presented study cohort, infant measles-binding antibody levels exceeded maternal levels at birth, with a median of just under 2,048 mIU/mL in infants compared with approximately 1,024 mIU/mL in mothers. By 2 months, median levels dropped to 512 mIU/mL. Seropositivity declined from 89.1% at 2 months to 8.7% at 6 months for the Edmonston strain, from 91.3% to 19.6% for the B3 strain, and from 91.3% to 17.4% for the D8 strain.
Creech presented historical data showing that mothers born before 1967 possessed substantially higher neutralizing antibody concentrations ranging from 2,048 mIU/mL to 4,096 mIU/mL, compared with mothers born after 1967 whose median concentrations fell below 1,024 mIU/mL.
Modeling indicated that newborns of mothers born before 1967 maintained estimated protection for 5.9 months, whereas newborns of mothers born after 1967 retained protection for roughly 3.9 months. Creech suggested that vaccination of younger infants, such as at 9 months of age, might be warranted in the context of higher measles circulation, especially if the US loses its measles elimination status.
“I would posit that the data from this study would suggest that vaccination of younger infants, such as 9 months of age, might be warranted in the context of higher measles circulation, especially if we lose our measles elimination status,” noted C. Buddy Creech, MD, MPH, who serves as professor of medicine at Vanderbilt Medicine and pediatric infectious diseases director of the Vanderbilt Vaccine Research Program.
Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.