Muyabia Labony; Dbarta24 — Infants under nine months old—who are too young to receive their first routine dose of the measles-rubella (MR) vaccine—are bearing the heaviest burden of the ongoing measles outbreak in Bangladesh, according to a primary study by icddr,b and the Bangladesh Shishu Hospital and Institute.
The joint investigation, which analyzed hospital admissions and viral genetics, confirmed that the highest infection rates were concentrated among infants aged between 3 and 8 months.
Crucially, researchers also confirmed that there is no evidence of genetic mutation in the circulating measles virus that would allow it to evade existing vaccines.
Maternal Antibodies Fade, Leaving Infants Exposed
In Bangladesh, the standard national immunization schedule dictates that the first dose of the MR vaccine is administered at nine months of age. Before this milestone, infants rely primarily on maternal antibodies passed down during pregnancy.
However, researchers highlighted that these natural antibodies wane rapidly within the first few months of life, leaving children aged 3 to 8 months in a critical gap where natural protection has vanished and vaccine protection has not yet begun.
The study observed 341 suspected measles patients under 14 years of age who were admitted to the hospital between April 20 and May 21. Laboratory testing confirmed measles in 324 of these cases.
Infection Breakdown by Vaccination Status:
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Unvaccinated (Under 9 Months): Out of 146 infants ineligible for vaccination, 142 (97.3%) tested positive. The 3–8 month age group saw 137 positive cases out of 141 tested.
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Eligible but Unvaccinated: Out of 126 children who were old enough but had received no vaccine doses, 122 (97%) tested positive.
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Single-Dose Recipients: Out of 48 children who had received one dose, 44 (92%) tested positive.
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Two-Dose Recipients: Out of 21 children fully vaccinated with two doses, 16 (76%) tested positive.
Researchers noted that the significantly lower infection rate among two-dose recipients aligns with expected vaccine protection parameters, though further investigation is required to understand breakthrough infections.
No Evidence of Vaccine-Evading Mutations
To assess whether a mutated strain was driving the sudden surge, scientists sequenced 55 full measles virus genomes (18 sequenced by icddr,b and 37 by the Institute of Epidemiology, Disease Control and Research – IEDCR).
The genomic analysis confirmed that all samples belonged to the B3 genotype, a strain currently circulating in several global outbreaks. While four minor mutations were identified in the epitope region of the virus’s H protein, researchers stressed these are not new and have been documented globally before.
“With a major outbreak, public concern regarding vaccine efficacy is natural. However, our investigation found no evidence that the virus is escaping vaccine protection,” said Dr. Nurjahan Maliha, Associate Scientist at icddr,b’s Virology Laboratory. “While infection rates were lower in two-dose recipients, the 16 cases where children contracted measles despite receiving two doses warrant deeper investigation.”
Addressing Gaps in Coverage and Immunity
Health experts emphasize that vaccination remains the single most effective defense against measles, but questions remain as to why localized outbreaks are occurring despite high national vaccination averages.
“Detailed research is ongoing to determine why some vaccinated children fall ill, what risk factors contribute to severe illness and mortality, how malnutrition impairs immunity, and precisely when maternal antibodies vanish,” stated Dr. Tahmeed Ahmed, Executive Director of icddr,b.
Adding to the call for action, Dr. Mustafizur Rahman, Senior Director of the Infectious Diseases Division at icddr,b, noted that while national coverage figures appear strong, public health authorities must examine why this outbreak reached such scale.
Complementing this view, Assistant Scientist Dr. Kamrun Nahar stressed the need to identify why individual children are missing doses and whether hidden pockets of low immunity exist behind national statistical averages.