Measles Virus Remains Vulnerable to Vaccines, icddr,b Study Confirms

Preliminary findings from an icddr,b investigation confirm that measles virus strains circulating in the country show no genetic changes capable of reducing vaccine protection, addressing public questions driven by the scale of the recent outbreak. According to an icddr,b press release issued today, researchers examining hospital admissions found that children who received both recommended doses were less likely to test positive among suspected cases, and genetic analysis identified the circulating strain as the B3 genotype.

Measles Outbreak Findings and Vaccine Efficacy Data

Researchers from icddr,b and the Bangladesh Shishu Hospital and Institute (BSH&I) investigated 341 children aged up to 14 years admitted to the hospital with suspected measles between April 20 and May 21. Laboratory testing confirmed measles in 324 of those children, according to the research team.

The investigation divided the 341 children into four distinct groups based on age and vaccination status. Among 146 infants below nine months of age—who were too young for routine immunization—142 tested positive, representing 97 percent of that group. Among 126 children who were old enough for vaccination but received no doses, 122 tested positive, or 97 percent.

For children who received partial or full immunizations, positivity rates dropped. Out of 48 children who received one vaccine dose, 44 tested positive, or 92 percent. Among 21 children who received both recommended doses, 16 tested positive, or 76 percent.

According to icddr,b, this 76 percent figure does not mean that 76 percent of all fully vaccinated children in the general population are contracting measles. Every child in the study had already been admitted to the hospital with suspected measles, meaning the percentage applies exclusively to the 21 fully vaccinated suspected patients in this hospital cohort. However, the progressively lower positivity rate—dropping from approximately 97 percent in unvaccinated children to 76 percent in fully vaccinated children—is consistent with vaccination providing active protection.

Evaluating Breakthrough Infections and Infant Vulnerability

The confirmation of measles in 16 fully vaccinated children requires further study, according to icddr,b researchers. Potential explanations include individual immune response variations where some children fail to develop strong protection, waning antibody levels over time, malnutrition, or other underlying health factors.

The findings also underscore a window of vulnerability for very young infants. In Bangladesh, the first routine measles-rubella vaccine is administered at nine months, with the second dose given at 15 months. Before the first dose, infants rely on maternal antibodies and community protection from broad vaccination coverage.

An initial analysis of stored samples from 16 mother-child pairs in an earlier icddr,b birth cohort showed that maternal measles antibodies declined rapidly during the first months of life. No protective antibodies were detected at three to eight months of age in that small group, though researchers note that a larger birth cohort sample is necessary to confirm population-wide trends.

“The size of this outbreak has understandably raised concerns about whether the vaccine is still working. Our findings provide no evidence that the virus has escaped vaccine protection,” said Noorjahan Maliha, associate scientist in the Virology Laboratory of the Infectious Diseases Division at icddr,b. She added that while lower positivity was observed among fully vaccinated children, the hospital-based study cannot provide a population-level estimate of overall vaccine effectiveness.

Future Research and Public Health Guidance

The researchers emphasised that the parents should not delay or avoid vaccination.

“Vaccination remains the most effective way to prevent measles and reduce the risk of severe illness. At the same time, we need to understand why this outbreak became so large despite comparatively high reported national vaccination coverage,” said Mustafizur Rahman, senior director of the Infectious Diseases Division at icddr,b.

To address lingering questions, icddr,b is developing an expanded research initiative. Tahmeed Ahmed, executive director of icddr,b, stated that the wider response will examine why certain vaccinated children contract the disease, which factors drive severe illness and mortality, how malnutrition influences protection, and the exact timeline of maternal antibody decay in infants.

In the interim, medical professionals urge parents not to delay routine immunizations. Caregivers should ensure children receive all eligible measles-rubella vaccine doses and adhere strictly to government health guidance during the outbreak.

Frequently Asked Questions

Does the recent measles outbreak mean the current vaccine is ineffective?

No. According to icddr,b preliminary findings, genetic analysis of the circulating B3 genotype shows no proof of mutations that allow the virus to escape vaccine protection.

Why did some fully vaccinated children test positive for measles?

Researchers note that breakthrough infections in fully vaccinated individuals can stem from factors such as an insufficient individual immune response, waning antibody protection over time, malnutrition, or other health variables requiring further study.

What is the recommended age for measles vaccination in Bangladesh?

The national immunization schedule administers the first routine measles-rubella vaccine dose at nine months of age, followed by a second dose at 15 months.

Are infants under nine months old protected against measles?

Infants under nine months are too young for routine vaccination and rely temporarily on maternal antibodies and community immunity, though icddr,b analysis suggests maternal antibodies may decline rapidly during the first months of life.