The cross-sectional study, led by Dr. Huy Quang Quach and colleagues, evaluated measles-specific antibody responses in 684 children and their 544 mothers from Kerala and Tamil Nadu between 2018 and 2023. Despite high vaccine coverage—where all children received at least two doses of a measles-containing vaccine and many received additional doses—the results highlighted significant immune response variability and evidence of ongoing viral circulation.
The following were the key findings of the study:
- 90.8% of children tested positive for measles-specific immunoglobulin G (IgG).
- 91.5% of children showed protective neutralizing antibody titers.
- 13% of vaccinated children had measles-specific immunoglobulin M (IgM), suggesting breakthrough infections and ongoing community virus circulation.
- Maternal antibody levels increased with age, indicating repeated exposure and continued measles transmission.
- Female children had significantly higher antibody titers than male children.
- Neutralizing antibody levels in children remained stable regardless of the number of vaccine doses, showing that extra doses did not necessarily strengthen immune responses.
One notable observation came from families with multiple children. Despite comparable IgG and neutralizing antibody levels, differing IgM profiles were detected among siblings, pointing to instances of recent or ongoing infection within the same household. This variability, according to the authors, highlights the complex dynamics of measles immunity and the challenges in relying solely on vaccine coverage as a measure of population protection.
For mothers, neutralizing antibody titers tended to rise with age, likely due to repeated exposure to the virus over the years. This pattern reinforced the conclusion that measles remains in circulation, even in regions with high vaccination rates.
The study emphasizes that while India has made remarkable strides in vaccine rollout, immunity gaps persist, potentially undermining elimination efforts. “These findings reveal that high vaccine coverage alone may not be sufficient to achieve measles elimination in India without a deeper understanding of why some children develop suboptimal immune responses,” the authors noted.
With India setting a target for measles elimination, the results underscore an urgent need to not only sustain immunization programs but also to investigate the biological, environmental, and epidemiological factors contributing to inadequate antibody responses. Without addressing these gaps, the researchers caution, measles elimination may remain out of reach despite robust vaccination campaigns.
"The study adds to growing evidence that achieving disease elimination requires more than widespread vaccination—it also demands strategies to enhance immune protection, monitor breakthrough infections, and curb community transmission," the authors concluded.
Reference:
Quach HQ, Jones SP, Joseph I, et al. Low Measles Seropositivity in Vaccinated Children. JAMA Netw Open. 2025;8(8):e2529409. doi:10.1001/jamanetworkopen.2025.29409
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